Question

英语语法问题

there are two buildings,( )stands nearly a hundred feet high.
我不懂为什么是要用 the larger of which,即为什么要用主语从句，而不能就用the large of them

Answer 1

这是一个（非限制性）定语从句，而不是主语从句。它修饰的是名词buildings。它是定语，而不是全句的主语。
which是关系代词，是介词of的宾语。
这句话也可以说成：
There are two buildings, of which the larger stands nearly a hundred feet high.
There are two buildings, which the larger of stands nearly a hundred feet high.

如果要换成the large of them，则前后两句话变成了并列关系，那么中间要用and连接。即：
There are two buildings, and the larger of them stands nearly a hundred feet high.
如果不用and连接，中间的逗号要改成句号。即：
There are two buildings. The larger of them stands nearly a hundred feet high.

Answer 2

这是一个非限制性定语从句，加个and就用the larger of them。
不加and是一个句子，后面的部分做定语，加and就是两个并列的句子。即：
There are two buildings, the larger of which stands nearly a hundred feet high.
There are two buildings, and the larger of them stands nearly a hundred feet high.