题目内容：

t is three years since he joined the League?it is three years since he has joined the League?
那个正确?为什么呢?

优质解答

It is three years since he joined the League. 这个正确
It is/has been +some time +since sb. did sth. 这是固定结构, " 自从某人做某事以来有...时间了." since从句中谓动只能用过去式.