高三英语知识点必修二：
since
从句的用法
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 e here.
自从她来到这里，就一直和我们住在一起。
.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
否认意 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 ...