since作状语时，主句可有以下六种时态：

一般现在时

It‘s a long time since they left.

他们已经离开很久了。

It‘s exactly a year since I startedworking here.

我来这里工作已经整整一年了。

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 twenty years since I‘ve seen her.

我已经二十年没见她了。

It‘s years since we last met.

我们多年没有见面了。

现在完成时

You‘ve grown since the last time Isaw you!

自从我上次见到你后，你又见长了！

It‘s been two weeks now since shecalled.

她到现在已经有两个星期没来电话了。

I left in 1990 and I haven‘t been back there since.

我于1990年离开那里，从那以后再也没有回去过。

Since he changed jobs he‘s looked like a new man.

他跳槽之后像换了一个人似的。

现在完成进行时

He‘s been working in a bank since leaving school.

他中学毕业以后一直在一家银行工作。

She‘s been working there since thebeginning of last summer.

她自从去年夏初起就一直在那里工作。

一般过去时

It was exactly five years since her father had died.

从她父亲去世到现在正好满五年。

过去完成时

He had been with the companysince its creation in 1989.

他从1989年公司成立以来，就一直在那里工作。

Since the party she had only spoken to him once.

那次聚会以后，她只和他说过一次话。

过去完成进行时

She had been waiting since five o’clock.

她从五点就开始等了