英语是现在世界上用的最多的一门语言，许多国家都在学英语和用英语，所以，学好了英语，出门就不怕沟通不方便了。精品学习网为大家推荐了高中英语学科知识点，请大家仔细阅读，希望你喜欢。

1. Since从句为非延续性动词的过去时或现在完成时，时间的起点应该从从句动作完成时刻算起。

例如：

Things have changed a lot since I wrote to you last time.

自我上次给你写信之后，情况已发生了很大的变化。

She has lived with us since she has come here.

自从她来到这里，就一直和我们住在一起。

2. Since从句为延续性动词的一般过去时，表示动作或状态的结束。其含义与动词的词义恰好相反，具有否定意味。

例如：

All has changed since he was at home.

自从他离开家以后，这里的一切都变了。

I haven’t written to her since she lived in London.

自从离开伦敦以来，我还没有给她写过信。

He has never been to see me since I was ill.

自从我病愈以来，他一直没有来看我。

Two years have passed since I last smoked.

我戒烟已经两年了。

但如果since从句是延续性动词的现在完成时，则表示动作由开始延续至说话的时候，具有肯定意味。

例如：

He has never been to see me since I have been ill.

自从我生病以来，他一直没有来看我。

She has talked little since she has stayed at home.

自从她呆在家里以后，就很少讲话。

Since we have owned a car， we have gone camping every year.

自从我们有了汽车后，年年都去野营。

3. 在现代英语中，since从句是延续性动词的一般过去时，有时候也可以表示肯定意味。此时，多半用ever来加强since的语义。

例如：

She has known me ever since she was a child.

她从小就认识我了。

I have live here ever since I was born.

我生下来就住在这里。

4. 在it is+时间+since从句结构中，since从句是非延续性动词的一般过去时，含有肯定意味。

例如：

It is three years since her husband left her.

她丈夫离开她已经3年了。

It is over sixty years since the People’s Republic of China was established.

中华人民共和国已经成立60多年了。

5. 在it is+时间+since从句结构中，since从句是延续性动词的一般过去时，含有否定的意味。

例如：

It is three years since she stayed here.

她离开这里已经3年了。

How long is it since you were a league member?

你退团有多久了?