The Reason That You Do Not Observe a Doppler Shift

Multiple Choice

The reason that you do not observe a Doppler shift when you listen to the car radio while driving is that

A) the source and observer are moving at the same speed.
B) the air inside the car is moving at the same speed as the car.
C) the speed of the car is too slow compared to the speed of sound.
D) the speed of the car is too fast compared to the speed of sound.
E) there is a Doppler shift but we don't notice it.