Sentence Correction

Nobody knows exactly how many languages there are in the world, partly because of the difficulty (of? ) distinguishing between a language and the sub-languages or dialects within it, but those who have tried to count typically have found about five thousand.

A) and the sub-languages or dialects within it, but those who have tried to count typically have found
B) and the sub-languages or dialects within them, with those who have tried counting typically finding
C) and the sub-languages or dialects within it, but those who have tried counting it typically find
D) or the sub-languages or dialects within them, but those who tried to count them typically found
E) or the sub-languages or dialects within them, with those who have tried to count typically finding

OA is A, what is wrong with C

the pronoun 'it' is wrongly used in C

Between is used hence we should use 'and' and not or...D and E are out...

B. counting typically finding.... wrong.

C. uses 'it' for the plural form 'sub-languages' and also 'find' is present tense, where the sentence is saying something about past...found is correct...

A. Perfect...