A string stretched between two fixed points sounds its second harmonic at frequency f.
![](https://www.iitianacademy.com/wp-content/uploads/2020/11/Schermafbeelding_2018-08-13_om_18.33.18.png)
Which expression, where n is an integer, gives the frequencies of harmonics that have a node at the centre of the string?
A. \(\frac{{n + 1}}{2}f\)
B. nf
C. 2nf
D. (2n + 1)f