并列句中如果前后分句有相同的部分，常常可以省略掉，以避免重复。通常被省略的可以是主语、谓语、谓语动词、宾语或其它成分，或句子成分的一部分。

约翰喜欢集邮，但不喜欢听音乐。（省略主语）John likes collecting stamps, but hates listening to music ,

John likes collecting stamps, but John hates listening to music ,

有些书是应当尝尝滋味的，有些书是应当吞食下去的，有少数书是应当咀嚼和消化的。（省略谓语）Some books are to be tasted，others to be swallowed，and some few to be chewed and digested ,

Some books are to be tasted，others are to be swallowed，and some few are to be chewed and digested ,

我到过北京，见到了万里长城。（省略主语+助动词）I have been to Beijing and seen the Great Wall ,

I have been to Beijing and I have seen the Great Wall ,

我请他去看电影，但他不想去。（省略作宾语的不定式）I asked him to see the film，but he didn't want to ,

I asked him to see the film，but he didn't want to see the film,

为了避免重复，不定式可以省去与句子前面重复的动词原形，但不定式符号 to 必须保留

 你愿意参加这项活动吗？Will you join in the game?,

我很乐意参加。I'd be glad to ,

I'd be glad to join in the game ,

我不想去那里，但不得不去。I didn't want to go there，but I had to,

I didn't want to go there，but I had to go there ,

我们能够，而且一定会在明天的比赛中获胜。（前一分句省略谓语+宾语）We can，and certainly will，win tomorrow's match,

We can win tomorrow's match，and certainly will，win tomorrow's match ,

我又想找到他，又怕找到他。I wished，yet feared to find him ,

I wished to find him，yet feared to find him ,

他们能够也应该支付全部费用。They can and should pay the full fee ,

They can pay the full fee and they should pay the full fee ,

我将飞往广州，但开车回来。I'll fly to，but drive back from Guangzhou,

I'll fly to Guangzhou，but I'll drive back from Guangzhou ,

很抱歉，我不能去。Sorry I couldn't go,

I'm sorry I couldn't go ,

 你没什么要补充吗？ Nothing more you want to say?

Is there nothing more you want to say?,

很遗憾，他失败了。Pity he's failed ,

it is a pity he's failed ,

如果他说来，他就一定会来。If he says he'll come，he will ,

If he says he'll come，he will come ,

 如果天下雨怎么办？What if it 's raining ?

What will happen if it 's raining?,

 那东西在哪里？Where is it?,

就在你放的地方。Where you left it ,

It is where you left it ,

 你的英语学得怎么样？How are you getting on with your English?,

没有我预计的那样好。 Not so well as I expected ,

I'm not getting on so well as I expected ,

 你很快要出国吗？Will you go abroad soon?,

要到明年夏天大学毕业后才出国。Not until I graduate from the college next summer ,

I'll not go abroad until I graduate from the college next summer ,

在一些状语从句中，如果谓语动词是 be ，主语又和主句的主语一致，或者主语是 it ，常常可以把从句中的主语和 be 省略掉。

以 when或者，while，或者once，或者until 等连词引导的时间状语从句，be 是助动词，可以把从句中的主语和助动词 be 省略掉。

入国问禁，入乡随俗。When in Rome, do as Rome does ,

When you are in Rome, do as Rome does ,

在任何可能的时间，你应多讲英语。（省略的主语 it 并不和主句的主语一致）Whenever possible，you should speak English as much as you can ,

Whenever it is possible，you should speak English as much as you can ,

请尽快来。Please come as soon as possible ,

Please come as soon as it is possible ,

由连词 before 和 after 引导的时间状语从句，如省略了主语和 be 之后， before 和 after 就成了介词。动词的 e d 形式不可做介词的宾语。

这台旧机器在使用前必须检查。动词的 e d 形式不可做介词的宾语The old machine must be checked before being used ,

The old machine must be checked before it is used ,

问了他三遍他才告诉我真相。He told me the truth after being asked three times ,

He told me the truth after he was asked three times ,

以 as if 或者as though 等连词引导的方式状语从句，be 是助动词，可以把从句中的主语和助动词 be 省略掉。

她躺在那儿，好像死了。（省略的主语和主句的主语一致）She lay there，as if dead ,

She lay there，as if she was dead ,

他张开嘴唇，好像要说什么话似的。He opened his lips as if to say something ,

He opened his lips as if he were going to say something ,

以 if 或者unless 等连词引导的条件状语从句， be 是助动词，可以把从句中的主语和助动词 be 省略掉。

如果方便的话，我们八点钟出发。We shall start at eight，if convenient,

We shall start at eight，if it is convenient ,

如果下面句子中有错，请加以改正。Correct the mistakes in the following sentences，if any ,

Correct the mistakes in the following sentences，if there are any ,

英语单词不经常重复是很容易忘记的。English words are easily forgotten unless constantly repeated,

English words are easily forgotten unless they are constantly repeated ,

以 even if 或者even though或者though或者although或者whether 等连词引导的让步状语从句， be 是助动词，可以把从句中的主语和助动词 be 省略掉。

甚至在五月底下霜也是可能的，虽然可能性不太大。Frost is possible，though not probable，even at the end of May ,

Frost is possible，though it is not probable，even at the end of May ,

不管任务是否艰巨，我们都要尽力去完成。Whether difficult or not，we will try our best to complete the task ,

Whether it is difficult or not，we will try our best to complete the task ,

不论原因是什么，结果是确定的。Whatever the cause，the result is certain ,

Whatever the cause may be，the result is certain ,

他虽然年轻但懂得很多。Though young，he knows a lot ,

Though he is young，he knows a lot ,

如果 be 是助动词，后面跟着现在分词或过去分词，只要主语和从句中的主语相同，可以把从句中的主语和助动词 be 省略掉。

他在骑马时伤了腿。He hurt his leg while riding a horse ,

He hurt his leg while he was riding a horse ,

骑车时，不要忘记看红绿灯。When cycling，don't forget the traffic lights ,

When you are cycling，don't forget the traffic lights ,

一旦看见，就永远不会忘记。Once seen，it can never be forgotten ,

Once it is seen，it can never be forgotten ,

橡胶如果燃烧起来，会发出有毒气体。If burnt，rubber can give off a poisonous gas,

If it is burnt，rubber can give off a poisonous gas ,