GMAT Sentence Correction (SC) | Nobody knows exactly how many languages there are in the

Nobody knows exactly how many languages there are in the world, partly because of the difficulty of distinguishing between a languageand 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 withinit , 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