问道非限定性定语从句的问题There are two buildings,the larger of which sta

the larger of是定语从句中主语的一部分.
把定语从句复原后是：The larger of the two buildings stands nearly a hundred feet high.
从句的完整主语是：The larger of the two buildings.
The larger of当然是主语的一部分了.
至于你问的先行词和关系代词之间还能插入成分的问题,这种现象在定语从句中是很常见的.举几个例子：
He loved his parents deeply,both of whom are very kind to him.
In the basket there are quite many apples,some of which have gone bad.
There are forty students in our class in all,most of whom are from big cities.

the larger of是修饰 two buildings 中的那个更大的，作定语。
这句的翻译：那儿两个建筑物，【更大的那个】近百英尺高，
从中文翻译中也可以看出the larger of是做修饰成分的。 the larger of which 是从句中的主语。
定语从句中，先行词和关系代词当然还能插入成分啊，如果从句中有介词，一般就把它提到关系代词之前，就会有of...

the larger of which是从句的主语啊，主句说了有two buildings，从句中的主语当然要有所限定啊。

把the larger of which 整个看成从句的主语就对了。