用法一：lt is/was+被强调部分+that/who+其他成分,被强调部分为“人”时可用who/that,被强调部分是事物时用that。
It is I who/ that am right.(主语)
It was him that/who we met at the school gate (宾语)
It was in the park that Tom lost his watch.(状语)
用法二：一般疑问句的强调句型是:Is/ Was it+被强调部分+that/who+其他成分。这种强调句的一般疑问句只需把is/was提前。如:
Was it in 1939 that the Second World War broke out?
第二次世界大战是在1939年爆发的吗?
用法三：特殊疑问句的强调句型:特殊疑问词+is/ was it that+其他成分。如：
Who was it that broke the window?
打破窗户的`是谁?
用法四：有时可用 It might be...that.…; It must have been...that...句型表示强调。如:
It might be his father that you're thinking of.
你想到的可能是他父亲。
用法五：not...until...结构的强调句型。如:
He didn't go to bed until ten o'clock
=It was not until ten o'clock that he went to bed