构成
强调句其实就是一个普通的句子一拆两半，用 It is 和 that 重新连接。
It is+ 句子中要强调的部分 +that+ 句子中剩下的部分
I want to go to American this summer.
// 强调 American
It is It is that I want to go to this summer.
从上面的案例可以看出，强调句其实是从定语从句演变而来的。但是演变到后来，强调句就不像定语从句那样只能修饰名词了。
They solved the problem until last week.
It was until last week that they solved the problem.
变化
It is/was+ 句子中要强调的部分 +that/who+ 句子中剩下的部分
只有强调的是人的时候，才可以用 who.
不能强调的部分
强调句不能强调形容词和动词。如果 It is 后接的是动词或形容词，那就变成主语从句了。
It is acknowledged that the internet has changed the world.
