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.