John is listening to a horn. He knows the frequency of the horn is 516.402 Hz when both he and the horn are at rest. If John hears the horn's pitch at 549.402 Hz, which of the following are possible?
A) Both can be moving and have the same speed.
B) Both can be moving while having di?erent speeds.
C) John can be moving toward a stationary horn.
D) The distance between John and the horn is increasing with time.
E) Both can be moving in the same direction.
F) Both can be moving, but away from each other.