If the girl is also near the source of the sound, two alike sets of sounds will be heard.
B is the correct answer . That make the most sense
To develop this problem it is necessary to apply the concepts related to the kinematic equations of motion. And from the speed found the relationships between wavelength, frequency and last of the period (which is inversely proportional to the frequency)
PART A) We know that the velocity of a body or a wave is equivalent to the distance traveled over a time interval. So,

Where
x = Distance
t = time


PART B) The frequency would then be defined as

Where



PART C) Finally the period is defined as




The rectilinear motion is given as:
s = s0 + v0 t + (1/2) a t^2
We can see that the variables stand for:
s = final distance
s0 = initial distance
v0 = initial velocity
t = time
a = acceleration
<span>We can see that all these variable are always constant
EXCEPT acceleration. The rectilinear motion can only be applied if and only if
acceleration is CONSTANT.</span>