6. 在it is+时间+since从句结构中，since从句是现在完成时或过去完成时，均含有否定意味。

例如：

It is five years since we have seen her.

我们已经5年没有见她了。

It was years since I had seen her.

在那之前，我已经有好久没有见到她了。

It’s been a long time since I’ve seen you.

我已经很久没有见到你了。

另外，①根据英语惯用法，since从句不可以否定形式出现。

例如：

It is four years since I have smoked a cigarette. 我已经4年不抽烟了。

不可说：It is four years since I haven’t smoked a cigarette.

但由于下句中的since不作“自从”解，所以从句可以用否定形式。

例如：

I haven’t been out anywhere since I don’t know how long.

也不知多久了，我哪儿也没去过。

②Since从句通常不与非延续性动词的现在完成时的肯定式连用。

例如：

Her mother died when she was a child.

她小时候母亲就去世了。

不可说：Her mother has died since she was a child.

③Since前不可加表示时间的词语，但可以与ago连用。

例如：

She has lived with us since her mother died three years ago.

自从她母亲3年前去世，她就一直和我们住在一起。

不可说：She has lived with us three years since her mother died.

④在It was five years ago since his father died. 一句中的since用错了，因为在含有ago的时间范畴里，已经有了从过去的一个时间点以来的时间，即已有了since的时间范畴，所以再用since是多余的。

改为：

It was five years ago that his father died.

他父亲5年前去世了。

It is five years since his father died.

他父亲去世已经5年了。

2016高考英语二轮复习since从句的用法讲解分享到这里，更多内容请关注高考英语考点栏目。

相关链接

2015-2016高考英语二轮复习宾语从句考点剖析 

2016年高考英语复习必备when引导的从句句型讲解