it was/is ...that/who...是强调句,但?

问题描述:

it was/is ...that/who...是强调句,但?
It is the young man____looked for____caught the murderer.
A that,who
B that,they
C they,that
D they,which
这个强调句能否理解为强调主语?Why?
那为什么A不行呢?
而且A才是真正强调主语啊?

是的