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Question 1

(a) Fig. 1.1 is a diagram of the female reproductive system in humans.
Identify the letters in Fig. 1.1 that represent the part:
that produces female gametes 
that receives the penis during sexual intercourse 
where fertilisation occurs. 
(b) State the names of the female gametes and the male gametes in humans.
(c) Gametes are cells.
Draw and label the main structures in a simple animal cell in the space provided.
(d) Circle the correct word or phrase in bold in each sentence to describe early development in humans.
During fertilisation, the nuclei of gametes fuse forming a fertilised cell called a fetus / a zygote / an embryo.
This divides to form a zygote / an embryo / an ovule which is a ball of cells.
This ball of cells implants into the wall of the cervix / uterus / vagina.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654, 2025–2027 syllabus):

• Topic B15.4 — Sexual reproduction in humans (Parts (a), (b), (d))
• Topic B2.1 — Cell Structure (Part (c))

▶️ Answer/Explanation

(a) produces female gametes = B; receives penis = D; fertilisation occurs = A

B is the ovary, which produces eggs (ova).
D is the vagina, which receives the penis during intercourse.
A is the oviduct (fallopian tube), the usual site of fertilisation.

(b) female gametes = ovum/egg; male gametes = sperm

Gametes are the specialised sex cells produced by meiosis.
In humans these are the ovum (egg) in females and sperm in males.

(c) Animal cell: cell membrane, nucleus, cytoplasm

A correctly drawn and labelled cell membrane forms the outer boundary of the cell.
The nucleus is drawn as a smaller circle inside, correctly labelled.
The region between the membrane and nucleus is labelled cytoplasm.

(d) a zygote; an embryo; uterus

Fusion of the nuclei of the sperm and egg during fertilisation produces a zygote.
The zygote divides repeatedly (mitosis) to form a ball of cells called an embryo.
The embryo implants into the wall of the uterus, where it continues to develop.

Question 2

(a) Air is a mixture of gases. Fig. 2.1 shows two pie charts representing samples of air, A and B.
(i) State which sample, A or B, represents clean air. Explain your answer.
(ii) Identify gas X.
(b) Sulfur dioxide is a common pollutant found in air.
(i) State one adverse effect of sulfur dioxide on the health of humans.
(ii) State one source of sulfur dioxide in the air.
(iii) State one other common pollutant gas found in the air.
(iv) Sulfur dioxide dissolves in rainwater to make acid rain. Suggest a pH value for acid rain.
(v) State the chemical substance used by farmers to treat soil acidity.
(c) An atom of sulfur has an electronic structure 2, 8, 6.
(i) On Fig. 2.2, complete the electronic structure for this atom of sulfur.
(ii) Suggest how many electrons this sulfur atom gains to become a sulfide ion \(S^{2-}\).

Most-appropriate topic codes:

• Topic C10.2 — Air quality and climate (Parts (a), (b))
• Topic C2.1 — Atoms and the Periodic Table, electronic structure (Part (c))

▶️ Answer/Explanation

(a)(i) Sample A; the proportion of gases (other than nitrogen) is correct for unpolluted air

Clean air is roughly 78% nitrogen, 21% oxygen and about 1% other gases.
Sample B shows an enlarged “other gases” segment, indicating pollution.

(a)(ii) Nitrogen

Gas X makes up the largest slice of both pie charts, matching nitrogen’s ~78% share of air.

(b)(i) Respiratory problems (e.g. asthma, bronchitis)

Sulfur dioxide irritates the airways and can worsen breathing conditions.

(b)(ii) Combustion of fossil fuels (containing sulfur) / volcanoes

Burning coal and oil that contain sulfur impurities releases \(SO_2\) into the air.

(b)(iii) Carbon monoxide or nitrogen oxides

These are other common gaseous pollutants produced mainly by vehicle engines.

(b)(iv) pH 3–6

Acid rain is more acidic than normal rainwater (pH ~5.6) due to dissolved \(SO_2\).

(b)(v) Lime/limestone \((CaCO_3)\), quicklime (CaO) or slaked lime \((Ca(OH)_2)\)

These basic compounds neutralise excess acid in soil.

(c)(i) 2, 8, 6 electron shells drawn

2 electrons in the first shell, 8 in the second shell and 6 in the third (outer) shell.

(c)(ii) 2 electrons

Sulfur has 6 outer electrons and needs 8 for a full outer shell, so it gains 2 electrons to form \(S^{2-}\).

Question 3

Fig. 3.1 shows four forces, A, B, C and D, acting on a submarine travelling underwater at a constant depth and at constant speed.
(a)(i) State the name of force C.
(ii) State how the magnitude of force B compares to the magnitude of force D.
(b) Sound above the maximum frequency that the healthy human ear can hear is called ultrasound. The submarine stops moving and then uses ultrasound to determine the depth of the sea floor.
(i) Suggest a value for the frequency of ultrasound.
(ii) Pulses of ultrasound waves are sent out through the water. The ultrasound pulses reflect off the sea floor and the reflection is detected by the submarine 1.4 s later.
Ultrasound waves move through sea water at a speed of \(1600 \text{ m/s}\).
Calculate the total distance travelled by the ultrasound pulse.
(iii) Use your answer to (b)(ii) to calculate the distance between the sea floor and the submarine.
(c) The submarine is powered by a nuclear reactor using the nuclear fission of the isotope uranium-235.
(i) State what is meant by the term isotope.
(ii) Describe what happens to the nucleus of a uranium-235 atom during nuclear fission.
(iii) Suggest one advantage of using nuclear fission to generate electricity.

Most-appropriate topic codes:

• Topic P1.5.1 — Forces (weight/upthrust, Part (a))
• Topic P3.4 — Sound, ultrasound (Part (b))
• Topic P5.1/P1.6.3 — The nucleus, nuclear fission and energy resources (Part (c))

▶️ Answer/Explanation

(a)(i) Weight

C acts downward on the submarine, which is the weight (gravitational force) acting on it.

(a)(ii) Equal

Since the submarine moves at constant speed, the forward force B equals the backward drag force D.

(b)(i) Above 20 000 Hz

Ultrasound is defined as sound with frequency higher than the upper limit of human hearing, ~20 kHz.

(b)(ii) 2240 m

Distance = speed \(\times\) time.
Distance \(= 1600 \times 1.4 = 2240\) m (total distance there and back).

(b)(iii) 1120 m

The pulse travels to the sea floor and back, so the one-way distance is half the total.
\(2240 \div 2 = 1120\) m.

(c)(i) Atoms of the same element with the same proton number but different nucleon number

Isotopes have identical chemical properties but differing numbers of neutrons.

(c)(ii) The nucleus splits

During fission, a uranium-235 nucleus splits into two smaller nuclei, releasing energy and neutrons.

(c)(iii) No \(CO_2\) emissions / high reliability

Nuclear fission does not release greenhouse gases during operation, unlike fossil fuels.

Question 4

(a) A student records their pulse rate in beats per minute (bpm) during different types of activity. Fig. 4.1 shows a bar chart of the results.
(i) Identify the activity that results in the smallest increase in pulse rate from the resting pulse rate.
(ii) Calculate the percentage increase in pulse rate from resting to running shown in Fig. 4.1.
pulse rate during rest …….. bpm
pulse rate during running …….. bpm
(b) The rate of aerobic respiration increases during exercise.
(i) State the two reactants in aerobic respiration.
(ii) Suggest why the rate of respiration increases during exercise.
(c) A hormone that causes pupils in the eye to widen also affects breathing and pulse rate.
(i) State the name of this hormone.
(ii) State the component of blood that transports hormones.

Most-appropriate topic codes:

• Topic B9.2 — Heart (pulse rate, Part (a))
• Topic B12.1 — Respiration (Part (b))
• Topic B13.2 / B9.4 — Hormones; blood (Part (c))

▶️ Answer/Explanation

(a)(i) Yoga

Comparing bar heights, yoga produces the smallest rise above the resting bar.

(a)(ii) 106%

Resting pulse rate = 68 bpm; running pulse rate = 140 bpm.
Percentage increase \(= \dfrac{140-68}{68}\times 100 \approx 106\%\).

(b)(i) Glucose and oxygen

These are the two reactants combined in aerobic respiration to release energy.

(b)(ii) More energy is needed for muscle contraction, so respiration releases more energy

Exercising muscles require extra energy, so the rate of aerobic respiration increases to meet demand.

(c)(i) Adrenaline

Adrenaline is the “fight or flight” hormone that widens pupils, and raises heart and breathing rate.

(c)(ii) Plasma

Plasma is the liquid component of blood that transports hormones, ions and dissolved substances.

Question 5

Table 5.1 shows five compounds, A, B, C, D and E, and the formula of each compound.
(a)(i) State the compound from Table 5.1 that is an unsaturated hydrocarbon.
(ii) Describe the chemical test that distinguishes between a saturated hydrocarbon and an unsaturated hydrocarbon and state the results for each.
(b)(i) State the name of the two compounds from Table 5.1 that are possible products of the combustion of compound E.
(ii) State the name of the compound made when compound D reacts with steam.
(iii) State the name of the polymer made using compound D as a monomer.
(iv) Draw the structure of compound E, \(C_2H_6\).
(c) State the names of the two most common greenhouse gases from Table 5.1.

Most-appropriate topic codes:

• Topic C11.2 — Alkanes and alkenes, addition polymers (Parts (a), (b)(i)–(iv))
• Topic C10.2 — Air quality and climate, greenhouse gases (Part (c))

▶️ Answer/Explanation

(a)(i) D \((C_2H_4)\)

\(C_2H_4\) (ethene) has a C=C double bond, making it unsaturated.

(a)(ii) Test with aqueous bromine; saturated stays orange, unsaturated turns colourless

Bromine water is added to the hydrocarbon.
A saturated hydrocarbon (no double bond) leaves the orange colour unchanged.
An unsaturated hydrocarbon decolourises the bromine water.

(b)(i) Carbon monoxide and carbon dioxide

Combustion of ethane \((C_2H_6)\) can produce these two carbon-containing products, depending on oxygen supply.

(b)(ii) Ethanol

Ethene reacts with steam (catalytic hydration) to form ethanol.

(b)(iii) Poly(ethene)

Ethene monomers join by addition polymerisation to form poly(ethene), commonly known as polythene.

(b)(iv) \(H_3C\!-\!CH_3\) structure

A single C–C bond joins the two carbon atoms.
Each carbon has three hydrogen atoms attached.

(c) Carbon dioxide and methane

Both \(CO_2\) and \(CH_4\) trap outgoing infrared radiation, making them significant greenhouse gases.

Question 6

(a) Fig. 6.1 shows an incomplete circuit diagram.
(i) Complete the circuit diagram by
  • adding an ammeter to measure the current in lamp A
  • adding a voltmeter to measure the potential difference across lamp A.
(ii) Identify component X.
(b) Lamp A has a resistance of \(6.0\,\Omega\) and lamp B has a resistance of \(4.0\,\Omega\).
The current in lamp A is 1.2 A.
(i) Calculate the potential difference across lamp A.
(ii) Calculate the combined resistance of the two lamps connected in series.
(iii) The two lamps are now connected in parallel. Their combined resistance is different.
Identify from the list the combined resistance of the two lamps connected in parallel.
Explain your answer.
2.4Ω    4.0Ω    6.0Ω    10Ω    24Ω
(c) In lighting circuits in houses, lamps are connected in parallel.
State two advantages of using lamps connected in parallel rather than in series.

Most-appropriate topic codes:

• Topic P4.3.1 — Circuit diagrams and components (Part (a))
• Topic P4.2.4 / P4.3.2 — Resistance; series and parallel circuits (Parts (b), (c))

▶️ Answer/Explanation

(a)(i) Ammeter in series with lamp A; voltmeter connected across lamp A

The ammeter must be in the main current path (series) to measure current through lamp A.
The voltmeter connects across (in parallel with) lamp A to measure the p.d. across it.

(a)(ii) Variable resistor

The zig-zag symbol with an arrow through it represents a variable resistor (rheostat).

(b)(i) 7.2 V

Using \(V = IR\):
\(V = 1.2 \times 6.0 = 7.2\) V.

(b)(ii) 10.0 Ω

In series, resistances add: \(6.0 + 4.0 = 10.0\,\Omega\).

(b)(iii) 2.4 Ω

The combined resistance of resistors in parallel is always less than the smallest individual resistance.
Only 2.4 Ω satisfies this, since it is lower than both 6.0 Ω and 4.0 Ω.

(c) If one lamp fails the others stay lit; each lamp receives the full mains voltage

Parallel wiring means lamps operate independently, unlike series circuits where one failure breaks the whole circuit.
Each lamp also gets the full supply voltage, so it works at its rated brightness.

Question 7

(a) Horses are herbivores. Define the term herbivore.
(b) Fig. 7.1 is a photograph of the lower jaw of a horse.
(i) Identify the type of teeth labelled X and Y in Fig. 7.1.
(ii) Identify the type of teeth found in a human jaw but not present in the jaw shown in Fig. 7.1.
(iii) State the name of the type of digestion that takes place using teeth.
(c) The statements describe some processes that occur in the alimentary canal.
Place ticks (✓) to show all the statements that describe the process of absorption.
(d) Complete these sentences about biological molecules.
Choose words or phrases from the list.
Each word or phrase may be used once, more than once or not at all.
amino acids       fatty acids        glycerol       glycogen       starch
Proteins are made from smaller molecules called ……. .
Glucose is used to make two larger molecules called ……. and ……. .
Iodine solution is used to test for the presence of ……. .

Most-appropriate topic codes:

• Topic B18.2 — Food chains and food webs, herbivore (Part (a))
• Topic B7.2/B7.3 — Digestive system, physical digestion, absorption (Parts (b), (c))
• Topic B4 — Biological molecules (Part (d))

▶️ Answer/Explanation

(a) An animal that gets its energy from eating plants

Herbivores obtain all their nutrients and energy solely from plant material.

(b)(i) X = premolars; Y = incisors

X labels the flat back teeth used for grinding (premolars/molars region).
Y labels the front cutting teeth (incisors).

(b)(ii) Canines

Horses (herbivores) generally lack the pointed canine teeth that humans (omnivores) have for tearing meat.

(b)(iii) Mechanical digestion

Teeth physically break food into smaller pieces without any chemical change, so this is mechanical (physical) digestion.

(c) 

Absorption is defined as nutrients moving from the intestine into the bloodstream.
The other statements describe digestion, assimilation or ingestion, not absorption.

(d) amino acids; glycogen and starch; starch

Proteins are built from amino acid monomers.
Glucose is stored/joined to form the two polysaccharides glycogen (animals) and starch (plants).
Iodine solution turns blue-black in the presence of starch.

Question 8

(a) Table 8.1 gives statements about molecules in solids and gases.
Put a tick (✓) next to each statement to show if it refers to a solid or to a gas.
(b) Use the list of substances to answer the following questions.
Each substance may be used once, more than once or not at all.
carbon      chlorine      copper      ethanol      oxygen      water
(i) Identify one substance which is a compound.
(ii) Identify two substances which are solvents.
(iii) Identify one substance which is a transition element.
(iv) Identify one substance which is a halogen.
(v) Identify one substance which consists of diatomic molecules.

Most-appropriate topic codes:

• Topic C1.1 — Solids, liquids and gases (Part (a))
• Topic C8.4 — Transition elements (Part (b))

▶️ Answer/Explanation

(a)

In solids, particles are held tightly together and can only vibrate in place.
In gases, particles are far apart and move freely and randomly.

(b)(i) Water (or ethanol)

A compound contains two or more different elements chemically joined; water \((H_2O)\) is a compound.

(b)(ii) Ethanol and water

Both ethanol and water are common liquids used to dissolve other substances (solvents).

(b)(iii) Copper

Copper is located in the transition metal block of the Periodic Table.

(b)(iv) Chlorine

Chlorine is in Group VII, the halogens.

(b)(v) Chlorine or oxygen

Both chlorine \((Cl_2)\) and oxygen \((O_2)\) exist as diatomic molecules made of two atoms.

Question 9

(a) Train track is made of lengths of steel rails with small gaps between them.
Fig. 9.1 shows some train track.
(i) Suggest why gaps are left between the steel rails.
(ii) A steel rail has a volume of \(0.13\,\text{m}^3\).
The density of steel is \(7900\,\text{kg/m}^3\).
Calculate the mass of the steel rail.
(b)(i) A train travels along the track for 600 s.
The train starts from rest and accelerates to a speed of 12.5 m / s in 200 s.
The train then travels at a constant speed for 300 s before slowing down and stopping after a further 100 s.
Complete the speed–time graph shown in Fig. 9.2 to show the motion of the train.
(ii) During the journey, the train engine transfers \(5 \times 10^{9}\) J of energy to the train.
State the work done on the train by the engine.
(c) Nuclear waste is carried by trains.
Nuclear waste emits ionising radiation.
(i) State one harmful effect of ionising radiation on human health.
(ii) Suggest how the nuclear waste is stored safely during the train journey.
(d) The headlamps of a train produce visible light.
Visible light is part of the electromagnetic spectrum.
Fig. 9.3 shows an incomplete electromagnetic spectrum.
Complete Fig. 9.3 to show all the parts of the electromagnetic spectrum.

Most-appropriate topic codes:

• Topic P1.4 — Density (Part (a))
• Topic P1.2 / P1.6.2 — Motion, work done (Part (b))
• Topic P5.2.5 — Applications and safety of radioactivity (Part (c))
• Topic P3.3 — Electromagnetic spectrum (Part (d))

▶️ Answer/Explanation

(a)(i) To allow for thermal expansion of the rails

Metals expand when heated; gaps prevent the rails buckling or being damaged in hot weather.

(a)(ii) 1027 kg

Using \(mass = density \times volume\):
\(mass = 7900 \times 0.13 \approx 1027\) kg.

(b)(i) Straight line rising to 12.5 m/s at 200 s, horizontal to 500 s, then falling to zero at 600 s

The line stays level at 12.5 m/s for the 300 s constant-speed section.
It then decreases steadily to zero over the final 100 s.

(b)(ii) \(5 \times 10^{9}\) J

Work done equals the energy transferred by the engine, so work done \(= 5 \times 10^9\) J.

(c)(i) Cancer or radiation burns

Ionising radiation can damage cells, causing mutations that may lead to cancer.

(c)(ii) Stored in a lead-lined container

Thick lead shielding absorbs the radiation, protecting people from exposure during transport.

(d) 

The spectrum is arranged in order of increasing frequency: radio waves have the lowest frequency and gamma rays the highest.
The missing regions between X-rays and infrared are ultraviolet and visible light; after microwaves comes radio waves.

Question 10

(a) A student investigates the conditions required for the germination of seeds.
Fig. 10.1 shows the apparatus and conditions.
Only the seeds in test-tube A germinate.
State why the seeds in test-tubes B, C and D do not germinate.
(b) After germination, the shoots of the new plant grow towards the light.
(i) State the name of this tropic response.
(ii) Explain why plants grow towards light.
(c) Table 10.1 shows some of the names of the different layers of a leaf.
Complete Table 10.1.

Most-appropriate topic codes:

• Topic B15.3 — Sexual reproduction in plants, germination (Part (a))
• Topic B13.1 — Coordination and response, tropisms (Part (b))
• Topic B6.2 — Leaf structure (Part (c))

▶️ Answer/Explanation

B – no water/moisture; C – no oxygen; D – no suitable warmth

B has dry cotton wool, so the seeds lack the water needed for germination.
C has boiled, cooled water sealed under oil, which excludes dissolved oxygen.
D is kept in a refrigerator, too cold for the enzymes needed for germination to work effectively.

(b)(i) Phototropism

Phototropism is the growth response of a plant shoot toward a light source.

(b)(ii) To maximise light exposure for photosynthesis

Growing toward light increases the light energy available to the plant.
This light energy is needed to drive photosynthesis.

(c) Cuticle (top); palisade mesophyll (middle)

The waxy cuticle sits above the upper epidermis to reduce water loss.
The palisade mesophyll layer, packed with chloroplasts, lies just below the upper epidermis.

Question 11

(a) A student investigates the reaction between magnesium and dilute sulfuric acid. During the reaction, hydrogen gas and a salt are made.
(i) Complete the word equation for this reaction.
(ii) The reaction is exothermic.
Describe two observations which show that a chemical reaction occurs between magnesium and dilute sulfuric acid.
(iii) The hydrogen made in the reaction exists as molecules of hydrogen, \(H_2\).
Draw a dot-and-cross diagram to show the bonding in a molecule of hydrogen, \(H_2\).
(b) The formula of sulfuric acid is \(H_2SO_4\).
(i) State the number of different elements shown in this formula.
(ii) State the total number of atoms shown in this formula.
(c) Magnesium is a metal.
(i) Describe two physical properties of metals.
(ii) Table 11.1 shows the percentage composition of a magnesium alloy.
Calculate the mass of magnesium contained in 50 kg of the alloy.
Show your working.

Most-appropriate topic codes:

• Topic C9.4 — Reactivity series (Part (a))
• Topic C2.5/C3.1 — Covalent bonding, formulas (Parts (a)(iii), (b))
• Topic C9.1 — Properties of metals (Part (c))

▶️ Answer/Explanation

(a)(i) sulfuric acid + magnesium → hydrogen + magnesium sulfate

Metal + acid reactions produce a salt (magnesium sulfate) and hydrogen gas.

(a)(ii) Temperature rises; fizzing/bubbles are seen

The exothermic reaction causes the mixture to get hot.
Effervescence (bubbling) shows hydrogen gas is being produced.

(a)(iii)

Each hydrogen atom contributes one electron.
The single shared pair forms a covalent bond between the two atoms.

(b)(i) 3 elements

\(H_2SO_4\) contains hydrogen, sulfur and oxygen — three different elements.

(b)(ii) 7 atoms

2 hydrogen + 1 sulfur + 4 oxygen atoms \(= 7\) atoms in total.

(c)(i) Good conductor of electricity; good conductor of heat (or high melting point, malleable)

Metals such as magnesium are typically good conductors of both electricity and heat.

(c)(ii) 48 kg

Magnesium percentage \(= 100 – 3.0 – 1.0 = 96\%\).
Mass of magnesium \(= 0.96 \times 50 = 48\) kg.

Question 12

(a) A cyclist is riding a bicycle around a circular track.
The length of the track is 400 m.
The cyclist completes five laps of the track.
The time taken for each lap is measured and recorded in Table 12.1.
(i) Calculate the average time for one lap.
(ii) The air in the tyres warms up during the ride.
Describe how the motion of the gas molecules in the tyres changes during the ride.
(iii) Select the correct word from the list to complete each sentence.
solids      liquids      gases
          ………………………… have no definite shape or volume.
          ………………………… have a definite volume but take the shape of the container.
(b) Fig. 12.1 shows a cyclist near a road junction.
A car driver at the junction can see the reflection of the cyclist in a plane mirror.
The ray of light shown allows the car driver to see the cyclist approaching the junction.
(i) On Fig. 12.1, draw an arrow on the ray of light to show the direction of travel of the ray of light.
(ii) On Fig. 12.1, label the angle of incidence with the letter i.
(c) The bicycle is left outside on a sunny day. Energy from the Sun heats the metal frame of the bicycle.
(i) State the method of energy transfer between the Sun and the Earth.
(ii) State the method of energy transfer through the frame of the bicycle.
(iii) Describe a simple way of testing whether the frame is made from steel or from aluminium.

Most-appropriate topic codes:

• Topic P1.2 / C1.1 — Motion, average speed; states of matter (Part (a))
• Topic P3.2.1 — Reflection of light (Part (b))
• Topic P2.3.3 / P2.3.2 — Radiation, conduction; magnetism test for steel (Part (c))

▶️ Answer/Explanation

(a)(i) 35.3 s

Average \(= \dfrac{35.3+34.7+37.2+35.0+34.3}{5} = 35.3\) s.

(a)(ii) Molecules move faster

As temperature increases, the gas particles gain kinetic energy and move faster.

(a)(iii) Gases; liquids

Gases have no definite shape or volume, expanding to fill their container.
Liquids have a fixed volume but take the shape of their container.

(b)(i) Arrow pointing away from the cyclist, toward the driver

Light travels from the cyclist, reflects off the mirror, and travels onward to the driver’s eye.

(b)(ii) Angle between the incident ray and the normal, labelled i

The angle of incidence i is measured between the incoming ray and the normal line at the mirror surface.

(c)(i) Radiation

Energy travels from the Sun through the vacuum of space as electromagnetic (thermal) radiation.

(c)(ii) Conduction

Heat is transferred through the solid metal frame by conduction, via vibrating particles passing on energy.

(c)(iii) Test with a magnet; steel is attracted, aluminium is not

A magnet placed near the frame will attract steel (a magnetic material) but not aluminium (non-magnetic).

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