Question

He has two sons,both of whom works as physician.

这里both of....as physician都是定语从句，这里为什么用whom，whom在定语从句中充当宾语，但很显然这里both of whom是主语啊？

Answer 1

不可。如果改成them，那么both of them are teachers就是一句完整句子，一个逗号是不可连接两个句子的，如果改为He has two sons and both of them are teachers.就可以了。