____that called this morning?为什么只能用who is it

问题描述:

____that called this morning?为什么只能用who is it

这里是强调句
It is ...that 的句型.
本来是
who called this morning?
加上强调的部分就只能是
who is it that called this morning?
早上究竟是谁打的电话?