有一读者问： 如何做这道题：
(1)— What was the party like?
— Wonderful. It's years_________I enjoyed myself so much.
A. after B. when C. before D. since
应选D，即连词since。为什么只能选since呢？ 这是因为“It is（美国英语用has been）+表时间的名词+since引导的状语从句”是一个固定的句型，句型中的连词since不可更换作别的连词。since在此的意思是“自从”。再如：
(2)It's two years since I left school. （也可说Two years have passed since I left school）
since引导的从句有时亦可用现在完成时，如：
(3)It's a long time since I've seen you.
