There are altogether fifty students in our class,twenty（） are boys.A、of them B、of those C、of

There are altogether fifty students in our class,twenty（） are boys.A、of them B、of those C、of
There are altogether fifty students in our class,twenty（） are boys.A、of them B、of those C、of

There are altogether fifty students in our class,twenty（） are boys.A、of them B、of those C、of
C是不是of whom?因为 前两项都不对 定语从句引导名词要用who,介词后为宾格whom