A bat is in pursuit of an insect. The bat is flying ... ...

    A bat is in pursuit of an insect. The bat is flying 10 m/s to the east, and the insect is flying 10 m/s to the east. If the bat emits a constant frequency sound of 30 kHz, what frequency will he detect?
(A) 29 kHz
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in 12. Sound