来源：网络 作者：匿名 2009-10-26 15:14:14
1）It is the first / second time.... that…结构中的从句部分，用现在完成时。例如：
It is the first time that I have visited the city. 这是我第一次访问这城市。
This is the first time （that） I've heard him sing. 这是我第一次听他唱歌。
注意：It was the third time that the boy had been late.
2）This is +形容词最高级+that…结构，that 从句要用现在完成时。例如：
This is the best film that I've （ever） seen. 这是我看过的最好的电影。
（1） ---Do you know our town at all? ---No, this is the first time I ___ here.
A. was B. have been C. came D. am coming
答案B. This is the first time 后面所加从句应为现在完成时，故选B。
（2） ---Have you ____ been to our town before? ---No, it's the first time I ___ here.
A. even, come B. even, have come C. ever, come D. ever, have come
（错）I have received his letter for a month.
（对）I haven't received his letter for almost a month.
I have lived here for more than twenty years.我住在这儿二十多年了。
I have lived here since I was born. 我从出生起就住在这儿了。
I worked here for more than twenty years. （我现在已不在这里工作。）
I have worked here for many years.（现在我仍在这里工作。）
1）（对） Tom has studied Russian for three years. = Tom began to study Russian three years ago, and is still studying it now.
2）（错） Harry has got married for six years. = Harry began to get married six years ago, and is still getting married now.
显然，第二句不对，它应改为 Harry got married six years ago. 或 Harry has been married for six years.
1） since +过去一个时间点（如具体的年、月、日期、钟点、1980, last month, half past
I have been here since 1989. 1989起，我一直在这儿。
2） since +一段时间+ ago。例如：
I have been here since five months ago. 我在这儿，已经有五个月了。
3） since +从句。例如：
Great changes have taken place since you left. 你走后，变化可大了。
Great changes have taken place since we were here. 我们走后，变化可大了。
4） It is +一段时间+ since从句。例如：
It is two years since I became a postgraduate student. 我考上研究生有两年了。
He has completed the work. 他已完成了那项工作。 （表结果）
I've known him since then. 我从那时起就认识他了。（表经历）
2） 用于till / until从句的差异
He didn't come back until ten o'clock. 他到10 点才回来。
He slept until ten o'clock. 他一直睡到10点。
1. You don't need to describe her. I ___ her several times.
A. had met B. have met C. met D. meet
2. ---I'm sorry to keep you waiting.
---Oh, not at all. I ___here only a few minutes.
A. have been B. had been C. was D. will be