4.4 用于现在完成时的句型
1 ）It is the first / second time…. that… 结构中的从句部分，用现在完成时。
It is the first time that I have visited the city.
It was the third time that the boy had been late.
2 ）This is the… that… 结构， that 从句要用现在完成时 .
This is the best film that I've (ever) seen.
这是我看过的最好的电影。
This is the first time (that) I've heard him sing. 　这是我第一次听他唱歌。
典型例题
(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
答案 D. ever 意为曾经或无论何时，反意词为 never ，此两词常用于完成时。 This is the largest fish I have ever seen. It is / was the first time +that-clause 的句型中，从句要用完成时。
[注意]: 非延续性动词的否定形式可以与表示延续时间的状语连用。即动作不发生的状态是可以持续的。
（错）I have received his letter for a month.
（对）I haven't received his letter for almost a month.
4.5 比较 since 和 for
Since 用来说明动作起始时间，for 用来说明动作延续时间长度。
I have lived here for more than twenty years.
I have lived here since I was born..
My aunt has worked in a clinic since 1949.
Some new oilfields have been opened up since 1976.
I have known Xiao Li since she was a little girl.
My brother has been in the Youth League for two years.
I have not heard from my uncle for a long time.
[注意]: 并非有 for 作为时间状语的句子都用现在完成时。
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。)
小窍门：当现在完成时 + 一段时间，这一结构中，我们用下面的公式转化，很容易就能排除非延续动词在完成时中的误使。
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.