Consider a source of sound S and an observer P. The frequency of sound source is `n_0`. The frequency heard by P is found to be
(1) `n_1` if P approaches S at speed v and S is stationary.
(2) `n_2` if S approaches P at speed v and P is stationary.
(3) `n_3` if each of P and S have speed `v//2` towards one another. Now,

Options

A. `n_1=n_2=n_3`
B. `n_1 gt n_2`
C. `n_3 ltn_0`
D. `n_3` lies between `n_1` and `n_2`