这里为什么不能用that?并且这里的which引导的是什么从句?

问题描述:

这里为什么不能用that?并且这里的which引导的是什么从句?
when young Tom cried,Father told him that tears were signs of being weak_B_ a man wasn't supposed to be
A that B which

which 引导的定语从句说明 tears were signs of being weak.而that 引导的只说明一个单词,显然不适合本句