a. It was Jim who met your sister in the zoo.
b. It was your sister that (whom) Jim met in the zoo.
c. It was in the zoo that Jim met your sister.
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.
It was Betty who had been wrong.
It's the people who we should rely on.
Was it you that broke the window?
b. It was on Monday night that this happened.
It was through me that he lost his place.
It was here that he differed from an Englishman .
It's my duty to help them.
Is it convenient to call you up tonight?
How long does it take to get there?
It's no use worrying about it.
It's dangerous playing with fire.
Is it worth while doing it?
It's good (that)you have thought of us.
It's happened that she wasn't in.