11.10 比较一般过去时与现在完成时
1）一般过去时表示过去某时发生的动作或单纯叙述过去的事情，强调动作；现在完成时为过去发生的，强调过
去的事情对现在的影响，强调的是影响。
2）一般过去时常与具体的时间状语连用，而现在完成时通常与模糊的时间状语连用，或无时间状语。
一般过去时的时间状语：yesterday, last week，…ago, in1980, in October, just
now等，皆为具体的时间状语。
现在完成时的时间状语：for, since, so far, ever, never, just, yet,
till/until, up to now, in past years, always等，皆不确定的时间状语。
共同的时间状语：this morning, tonight, this April, now, already,
recently, lately 等。
3）现在完成时可表示持续到现在的动作或状态，动词一般是延续性的，如live, teach, learn, work,
study, know.。
一般过去时常用的非持续性动词有come, go, leave, start, die, finish, become,
get married等。例如：
I saw this film yesterday. （强调看的动作发生过了）
I have seen this film. （强调对现在的影响，电影的内容已经知道了）
Why did you get up so early? （强调起床的动作已发生过了）
Who hasn't handed in his paper? （强调有卷子未交，疑为不公平竞争）
He has been in the League for three years. （在团内的状态可延续）
He has been a League member for three years. （是团员的状态可持续）
句子中如有过去时的时间副词（如yesterday, last, week, in
1960）时，不能使用现在完成时，要用过去时。
（错）Tom has written a letter to his parents last night.
（对）Tom wrote a letter to his parents last night.
11.11 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。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。
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。
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.
11.12 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。例如：
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。
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。）
注意：用句型转换的方法，很容易排除非延续动词在有for/since结构的完成时中的误用。
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.
