the old man has two sons,both of ()are lawyers,这个题目中逗号改为句号,那有什么不同呢?

the old man has two sons,both of (whom)are lawyers这是主从复合句,both of (whom)are lawyers是个非限制性定语从句比较：The old man has two sons.Both of (them)are lawyers这是两个独立分句,所以括号里面的用...定语从句中，介词在关系代词之前时， 指人只能用whom, 指物只能用which. 记住！！！第二个我说了是两个独立的句子了， 后面不是定语从句，当然不能用关系代词whom了。 更不能用who了