状语从句句首的It本身就是句子的主语；而强调句首的It不作任何成分也没有实际意义。
状语从句的连接副词that及句子前面的It be不能去掉
状语从句的引导词可以是when / where，而强调句型中的that不能用其他词代替。
英语强调句与状语从句的区别示例如：
1.It is such an interesting book that we all like it very much.
它是一本如此有趣的书，我们大家都非常喜欢。
注：结果状语主从复合句
2.It is such an interesting book that we all like very much.
我们大家都非常喜欢的就是一本如此有趣的书。
注：强调such an interesting book
比较：It is such an interesting book as we all like very much.
这就是我们大家都非常喜欢的有趣的书。
注：这是定语从句
3.It was already morning when he woke up.
当他醒来时，已经是早晨了。
注：时间主从复合句
It was the next morning that he woke up.
就在第二天早晨他醒来了。
