In human hearing, subtle differences in how the two ears hear a given sound help the listener determine the qualities of that sound.
A. in how the two ears hear a given sound help the listener determine
B. in the two ears hearing a given sound help the listener in determining
C. in how a sound is heard by the two ears helps the listener determine
D. between how the two ears hear a given sound helps the listener in determining
E. between how a sound is heard by the two ears help the listener in determining

This is GMATPREP question. I choose "B" but this not the answer. Pls help me identify what is wrong with "B" and what is the correct answer and why?

idiom: difference between
and "differences" in the sentence is plural , and hence requires "help"(plural verb)

Hence, choice E

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