$19.$ This one is pretty tricky. Using the form of the Doppler equation that solves for velocity, find the one true statement:

$v_e=\frac{fc}{2f_o(cos)}$

A$.$ If the operating frequency increases, the velocity estimate increases.

B$.$ If the cosine of the angle theta increases, the velocity estimate increases.

C$.$ If the frequency shift increases, the velocity estimate decreases.

D$.$ If angle theta increases, the velocity estimate decreases.

E$.$ If angle theta increases, the velocity estimate increases.