1) 两个动作如按顺序发生，又不强调先后，或用then，and，but 等连词时，多用一般过去时。 When she saw the mouse，she screamed. My aunt gave me a hat and I lost it. 2 ) 两个动作相继发生，可用一般过去时；如第一个动作需要若干时间完成，用过去完成时。 When I heard the news, I was very excited. 3) 叙述历史事实，可不用过去完成时，而只用一般过去时。 Our teacher told us that Columbus discovered America in 1492. 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 Ive (ever) seen.
这是我看过的最好的电影。
This is the first time (that) Ive heard him sing. 这是我第一次听他唱歌。
(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, its 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 received his letter for almost a month. 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.
