People in the north central region of the United States use

Aaah, there is already an Official explanation ... and it is much better than mine.

@devashish - I like that you offered your own explanation even in addition to the OE. It's important that you're thinking of why something is right/wrong, and often putting it into your own words is more helpful than what is "officially" written. As a teacher, I learned a long time ago that I couldn't teach nearly as well from the official explanations in the OG as I could from my own thought process, since my mind works a lot more similarly to students' minds than does the Official Guide editor's!

One pretty big strategic point that everyone can take away on this - if one or more of the answer choices uses "that of" or "those of", you have to make a decision about parallelism - you either need to have a possessive relationship or you don't, so you can specifically look for that.

Here, we need it: each answer choice already uses "their voice", and because there's a possessive quality to "their", then we need to use "that/those of" to get a proper comparison.

As you're scanning questions for decision points, the that/those of point is a good one to recognize!

It should be C.
'utterances' is plural and therefore B and E are out.
A and D have illogical comparison.