You hear 2 beats per second when two sound sources, both at rest, play simultaneously. The beats disappear if source 2 moves toward you while source 1 remains at rest. The frequency of source 1 is 500 Hz. The frequency of source 2 is...


A) 498 Hz.

B) 496 Hz.

C) 502 Hz.

D) 500 Hz.

E) 504 Hz.