The Diagram Shows Four Situations in Which a Source of Sound

Multiple Choice

The diagram shows four situations in which a source of sound S and a detector D are either moving or stationary. The arrows indicate the directions of motion. The speeds (when not zero) are all the same. (Note that the detector in situation 3 is stationary) . Rank the situations according to the apparent frequency of the source, lowest to highest.

A) 1, 2, 3, 4
B) 4, 3, 2, 1
C) 1, 3, 4, 2
D) 2, 1, 4, 3
E) None of the above