二者在句型结构上有很大的不同
强调句：其结构为：it is/was +被强调部 + that .
主语从句：
定义:如果一个句子在复合句中充当一个主语,那么这个句子就是主语从句.
（1)引导主语从句连词有that,whether,who,what,whatever等
（2)连词位于句首不能省略
例句：
What we need are good doctors.
Whom we must study for is a question of great importance.
What caused the accident remains unknown.
Whatever you did is right.
Whose watch was lost is unknown.
What we need is time.