Question

She had two sons,______ became teachers. A, both of them B both of whom 这两个答案到底有什么区别？

为什么选B 不选A 呢 ？

Answer 1

B both of whom
因为一个单句里只能有一个主干
She had two sons句子已经完整
所以如果选A，句子就有两个主干，错误
选B，定语从句修饰sons

Answer 2

这是从句，需要连词

Answer 3

如选A,去掉逗号，再加一个AND,也可以。这就是A与B 的区别。