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

A is the correct option.

which approach can i use to explain this? and why are you considering C as the right option?