It has been...（一段时间）+ since

It has been...（一段时间）+ since

It has been...（一段时间）+ since引导的从句/自从……以来已经……了

该句型中since引导的时间状语从句常用一般过去时。例如：

It's twenty years since he moved here.

他自从搬到这里已经20年了。

It has been six years since he married Mary.

他和玛丽结婚已经六年了。