"It looks as if从句"和“It's 3 years since 从句”两句的的IT的含义和用法?

问题描述:

"It looks as if从句"和“It's 3 years since 从句”两句的的IT的含义和用法?
请问下面这两个IT的含义和用法?
1 It's 3 years since 从句;
2 It look as if从句.
如果是形式主语,也不对啊,SINCE和AS IF引导的都不是主语从句,

It's 3 years since从句中,it是代词,指时间.
It look as if从句,该句型中it 无意义.As if 引导一个状语从句,常译为:“看起来好像……”如果与事实不相符合,则用虚拟语气.