since的用法时态用过去完成时

since的用法时态要看主句是什么时态如果主句是现在时或将来时,则since从句用现在完成时；若主句是过去式,则since从句用过去完成时。

since

prep.自…以后;从…以来;(表示气愤)何曾，什么时候；

conj.从…以后;自…以来;因为;由于;既然；

adv.自…以后;从…以来;此后;后来

It\'s a long time since they left.

他们已经离开很久了。

It\'s been two weeks now since she called.

她到现在已经有两个星期没来电话了。

I had been out since I was 17.

我从17岁起就公开我是同性恋。

The children are completely out of control since their father left.

这些孩子自他们的父亲离开后就无法无天了。

It\'s been an age since we\'ve seen them.

我们有很长一段时间没有见到他们了。