[求助]GWD-26-1

Nobody knews exactly how many language there are in the world, partly because of the difficulty of distinquishing between a language and the sub -languages or dialects within it ,but those woh have tried to count typically have found about five thousand 

B.and the sub -languages or dialects within them ,with those who have tried counting  typically finding.

答案是A,有哪位好心的人可以告訴我為什麼B不對??

還有答案中的IT指誰??

between a language and the sub -languages or dialects within it中的it 指a language.

B中with 后面一般不加从句.