A couple of things:
1. I am confused with 'it'. I originally suspected that 'them' would be more appropriate because of 'a language and the sublanguages...'. The plural 'sublanguages' had me confused. Should I have automatically assumed 'it' would be proper because of 'between' instead of 'among'?
2. I am also confused with the 2nd 'it' in answer choice (C). What's wrong with that?
Nobody knows exactly how many languages there are in the world, partly because of the difficulty of distinguishing between a language and the sublanguages or dialects within it, but those who have tried to count typically have found about five thousand.
(A) and the sublanguages or dialects within it, but those who have tried to count typically have found
(B) and the sublanguages or dialects within them, with those who have tried counting typically finding
(C) and the sublanguages or dialects within it, but those who have tried counting it typically find
(D) or the sublanguages or dialects within them, but those who tried to count them typically found
(E) or the sublanguages or dialects within them, with those who have tried to count typically finding
OA is A
1. I am confused with 'it'. I originally suspected that 'them' would be more appropriate because of 'a language and the sublanguages...'. The plural 'sublanguages' had me confused. Should I have automatically assumed 'it' would be proper because of 'between' instead of 'among'?
2. I am also confused with the 2nd 'it' in answer choice (C). What's wrong with that?
Nobody knows exactly how many languages there are in the world, partly because of the difficulty of distinguishing between a language and the sublanguages or dialects within it, but those who have tried to count typically have found about five thousand.
(A) and the sublanguages or dialects within it, but those who have tried to count typically have found
(B) and the sublanguages or dialects within them, with those who have tried counting typically finding
(C) and the sublanguages or dialects within it, but those who have tried counting it typically find
(D) or the sublanguages or dialects within them, but those who tried to count them typically found
(E) or the sublanguages or dialects within them, with those who have tried to count typically finding
OA is A
A sublanguage or dialect is part of what? A single language. Let's say you have a sublanguage X and a dialect Y. Could X be part of both English and German? Or could Y be part of both Swahili and Pig Latin? Not under normal circumstances. 
And let's say you have a sublanguage Z that is part of French. Would you have difficulty distinguishing between English and Z? Of course not. However, you might have difficulty distinguishing between "regular" French and Z. So, the meaning of the sentence is very important here. Once you figure out what the sentence is saying, then it becomes clear that "it" must be used to refer to "language." 
