the correct answer is A
This is a doppler effect exercise which is the change in frequency due to the relative movement of the sound source and the observer.
where v₀ is the speed of the observer and v_s the speed of the source, the signs correspond when the two are closing in
with this expression let's analyze the different answers
A) True. The observed change is in the frequency, in this case the two are moving away, so the expression that describes the phenomenon is
In this case, the speed of the source is greater than the speed of the observer, so when the denominator increases faster than the numerator, consequently the frequency must decrease
B) False. The amplitude does not depend on the relative velocity
C) False. The intensity depends on the distance, by or which when increasing the distance the intensity should decrease
D) False. The speed of sound is a constant, if the frequency decreases the wavelength must increase to maintain equality
E) False. The speed of sound depends on the properties of the propagating medium, not on the relative speed of the source and the observer.
Consequently the correct answer is A