"since" 是一个英语介词,用于表示从过去的某个时间点或事件开始一直到现在的一段时间。它在前后的用法和时态取决于它所连接的句子的时态。以下是一些常见的用法:
1. Since + 过去时间点:
Since 通常与过去时间点连用,表示从过去的某个时间点开始一直到现在的一段时间。例如:
- I have lived here since 2010. (我从2010年开始就住在这里。)
- She has worked at the company since she graduated. (她从毕业开始就在这家公司工作。)
2. Since + 过去事件:
Since 也可以与过去发生的某个事件连用,表示从那个事件开始一直到现在的一段时间。例如:
- I have known him since we were in high school. (我们从高中就认识了。)
- She has improved a lot since she started taking lessons. (自从开始上课以来,她已经进步了很多。)
3. Since + 持续动作:
Since 可以与持续动作连用,表示从某个动作开始一直到现在的一段时间。例如:
- I have been running since morning. (我从早上就开始跑步了。)
- She has been studying English since last year. (她从去年就开始学英语了。)
注意:当 since 引导的时间状语从句位于主句之前时,主句的谓语动词通常使用现在完成时。当 since 引导的时间状语从句位于主句之后时,主句的谓语动词通常使用过去式。例如:
- Since I have lived here, I have made many friends. (自从我住在这里以来,我交了很多朋友。)
- I have lived here since 2010. (我从2010年开始就住在这里。)