时间状语从句和省略

时间状语从句和省略
一、时间状语从句
1. 某些易用错的连词。

(1) 连词immediately / directly / instantly和词组the moment, the minute意为“一……就……”，相当于as soon as。

如：
The thief ran away the moment / directly he saw the policeman.
[注意]
a. immediately / directly / instantly也是副词，在句中作状语。

如：
I didn’t immediately realize how serious the situation was.
b. 介词on / upon +名词/ V-ing也表示“一……就……”。

如：
Yao Ming was surrounded by the media on his arrival at the airport.
On seeing the painting by Van Gogh, I fell in love with it at once.
(2) 词组the first time, the last time, each time, every time以及by the time，都引导时间状语从句。

如：
The first time I spoke English before foreigners, I was a student of high school.
Every time I meet the policeman at that crossroads, he will give me a big smile.
[注意] for the first time是介词短语，意为“第一次……”，常用来作状语。

They had a face-to-face talk for the first time.
(3) when, while和as引导时间状语从句的区别：
when引导时间状语从句时，可与短暂性动词连用，也可与延续性动词连用；而
while只能与延续性动词连用；as表示两个动作的同时性，意为“一边……，一边……”。

如：
When I entered the classroom, all the students looked up at me curiously.
Could you look after Robert while I am preparing the report?
The children sang as they climbed the mountain.
2. 时间状语从句中的时态。

(1) when, as soon as, every time, immediately, the moment等在引导时间状语从句时，若从句用一般现在时，主句用一般将来时。

如：
The moment I finish my homework, I will go out to play football.
(2) 在It / This / That is the first / second / last time that…中，that从句中的谓语动词用现在完成时；而It / This / That was the first / second / last time that…中，that从句中的谓语动词用过去完成时。

如：
This is the first time that I have visited the Great Wall.
That was the second time that he had been interrupted by the noise outside.
二、省略
1. 状语从句中的省略。

(1) 连词when, while, if, as, though / although, until, once, whether, unless, where等引导的状语从句中，当主句的主语和从句的主语一致时，常省略跟主句相同的主语和be，只剩下主要的部分。

如：
While / When (you are) crossing the street, you must be careful.
Unless (I am) invited to attend the party, I won’t go to his house.
(2) 当出现when, if, where, wherever, whenever, than等后直接接possible, necessary时，可理解为省略了“it + be的适当形式”。

类似的还有：if so, if not, if some, if any, if ever等。

如：
Please call me up if (it is) necessary. I relax with a good book whenever (it is) possible.
2. 不定式结构中的省略。

在同一个句子或紧密联系的对话中，为了避免重复，作宾语或补足语的不定式再次出现时，不定式符号后面的内容常被省略，只保留不定式符号。

常用于refuse, would like / love, wish, want, mean, expect, hope, intend以及afraid, happy, glad, willing, ready等后。

如：
Susan’s parents didn’t allow her to travel alone in Tibet, but she still hoped to (travel alone in Tibet).
[注意] 当to后是be或have 时，be与have 不能省略。

如：
—Is Miss Yang a doctor?
—No, but she used to be (a doctor).
—I haven’t handed in my homework yet.
—Well, you ought to have (handed in your homework).
3. 可以用so, not来替代上文或问句中的一部分或整个句子。

think, believe, guess,
suppose, hope等有这样的用法。

如：
—Can you finish the task ahead of time?
—I think so. / I think not. / I don’t think so.
4. 当不定式作表语时，若主句中出现do的各种形式，to可以省略。

如：
What we should do about the problem is (to) leave it alone.
[注意] 在have no choice but to do…句型中，to不省略，但若有do的各种形式，to可以省略。

如：
They had no choice but to wait for the police to come.
The child does nothing but play all day.
【巩固练习】
1. ______ Lang Lang was in his twenties, he had been a well-known pianist at home and abroad.
A. As soon as
B. Each time
C. For the first time
D. By the time
2. How long do you think it will be ______ the computer company can develop the household robot?
A. since
B. before
C. unless
D. that
3. — Have you got any plans for the coming Christmas holiday?
—Yes. ______, I’m going to visit China.
A. If not
B. If necessary
C. If possible
D. If so。