GMAT Sentence Correction (SC) | Re: In human hearing, subtle differences in how the two ears

First, it shouldn't be "help the listener to determine" (although that is how lots of people would say it). You don't need the "to" - and, if you don't need it, then it's not going to be in the correct answer!

Be careful about deciding based upon what sounds good or bad. The test will fool your ear. Go based upon the specific rules you KNOW are true.

You may read an original sentence and think it sounds awkward (in fact, this will happen quite a lot!), but if you cannot
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