The Diagram Shows the Various Positions of a Child in Motion

Multiple Choice

The diagram shows the various positions of a child in motion on a swing. Somewhere in front of the child a stationary whistle is blowing.
-At which position(s) will the child hear the same frequency as that heard by a stationary observer standing next to the whistle?

A) at both A and D
B) at B when moving toward A
C) at B when moving toward C
D) at C when moving toward B
E) at C when moving toward D