many of them算什么结构啊,为什么不能引导一个句子呢,many of whom就可以引导句子?

复习一下定语从句就很清楚了。
例子： There are 55students in our class. Many of them like watching soccer.
There are 55 students in our class, many of whom like watching soccer.
第一句是两句话；第二句是含有主从复句的一句话（whom 是关系代词，指代的是前面的55 students，在定语从句中做主语，因为在介词后，所以用WHOM，而不能用WHO引导）

many of them,是介词加代词的介宾结构,可以作句子的主语跟宾语.
many of whom,是介词加连接代词的结构,可以引导的是一个定语从句.