3．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. ①以when, while, once, until等连词引导的时间状语从句 When in Rome do as Rome does. 入国问禁.入乡随俗. Whenever possible, you should speak English as much as you can. 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) Please come as soon as possible. 请尽快来. 注意: 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. The old machine must be checked before it is used. 这台旧机器在使用前必须检查. [误]The old machine must be checked before used. (动词的-ed形式不可做介词的宾语) [正]The old machine must be checked before being used. He told me the truth after he was asked three times. 问了他三遍他才告诉我真相. [误]He told me the truth after asked three times. [正]He told me the truth after being asked three times. ②以as if, as though等连词引导的方式状语从句 She lay there, as if dead. 她躺在那儿.好像死了.(省略的主语和主句的主语一致) He opened his lips as if to say something. 他张开嘴唇.好像要说什么话似的. ③以if, unless等连词引导的条件状语从句 We shall start at eight, if convenient. 如果方便的话.我们八点钟出发. Correct the mistakes in the following sentences, if any. 如果下面句子中有错.请加以改正. English words are easily forgotten unless constantly repeated. 英语单词不经常重复是很容易忘记的. ④以even if, even though, though, although, whether等连词引导的让步状语从句 Frost is possible, though not probable, even at the end of May. 甚至在五月底下霜也是可能的.虽然可能性不太大. Whether difficult or not, we will try our best to complete the task. 不管任务是否艰巨.我们都要尽力去完成. Whatever the cause , the result is certain. 不论原因是什么.结果是确定的. Though young, he knows a lot. 他虽然年轻但懂得很多. 提示: 在这类从句中.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.也可以把从句中的主语和助动词be省略掉. He hurt his leg while riding a horse. 他在骑马时伤了腿. When cycling, don't forget the traffic lights. 骑车时.不要忘记看红绿灯. Once seen, it can never be forgotten. 一旦看见.就永远不会忘记. If burnt, rubber can give off a poisonous gas. 橡胶如果燃烧起来.会发出有毒气体. 【查看更多】
