1. it还可改变句子结构，使对句子的某一成分加以强调，如强调主语(a)，宾语(b)，状语(c)等：
a. It was Jim who met your sister in the zoo.
是吉姆在动物园碰到你妹妹的。
b. It was your sister that (whom) Jim met in the zoo.
吉姆在动物园里碰到的是你妹妹。
c. It was in the zoo that Jim met your sister.
吉姆是在动物园碰到你妹妹的。
2.强调部分指人时用who (m)，有时用that来引起后面从句(a)，其他情况都用that (b):
a. Lenin stressed that it is precisely the people who create history.
列宁强调说正是人民创造了历史。
It was Betty who had been wrong.
错的是贝娣?
It's the people who we should rely on.
我们应当依靠的是人民。
Was it you that broke the window?
打破窗子的是你吗?
b. It was on Monday night that this happened.
发生这事是在星期一夜里。
It was through me that he lost his place.
是因为我他才丢失这份工作的。
It was here that he differed from an Englishman .
他和英国人不同之处就在这里。
3.it还可用作为先行词作形式上的主语，把真正的主语移到句后，使句子显得平稳一些。后面真正的主语可以是：
l)不定式：
It's my duty to help them.
帮助他们是我的责任。
Is it convenient to call you up tonight?
今晚给你打电话方便吗?
How long does it take to get there?
到那里要多少时间?
2)动名词：
It's no use worrying about it.
发愁没有用。
It's dangerous playing with fire.
玩火是危险的。
Is it worth while doing it?
这样做值得吗?
3)从句：
It's good (that)you have thought of us.
难为你想到了我们。
It's happened that she wasn't in.
恰好她不在家。
