2010年12月大学英语四六级考试必备语法精要

　　7.非限制性定语从句

　　非限制性定语从句修饰先行词或整个主句，起补充说明的作用，如果省略掉，原句句意仍保持完整。非限制性定语从句要用逗号与主句隔开，其引导词不能用that。非限制性定语从句属于正式语体。经常考到的非限制性定语从句有以下三种。

　　1) 由which、as引导的非限制性定语从句。which、as代表整个主句。

　　He said that he had never seen her before, which was not true.

　　China is still a developing country, which is known to all of us.

　　2) 由 “介词+关系代词”引导的非限制性定语从句。

　　He sent her a letter, in which he said that he was sorry for what he had done to her.

　　He failed to pass the exam, because of which his parents scolded him.

　　4) 由 “数词、代词或名词+of +关系代词”引导的非限制性定语从句。

　　He had three sons, one of whom was my son’s classmate.

　　There are about twenty students in this course, most of whom are freshmen.

　　They are two different words, the spellings of which are easily confused.

　　Ⅱ 状语从句

　　1. 状语从句中以下四种从句考得较多，这里给予简单介绍。

　　1) 时间状语从句

　　时间状语从句主要由以下连词引导：when, whenever, as, while, since, until, till, before, after, as soon as, once, hardly (scarcely) … when, no sooner … than。

　　I will discuss the matter with you when we meet tomorrow.

　　He didn’t go to sleep until he finished doing his homework.

　　You have changed a lot since we met last time.

　　时间状语从句还可由某些可充当连词的名词(the moment, the instant, every time,等)和副词(instantly, directly等)引导：

　　I will tell you the news the instant I know.

　　Directly the teacher came in everyone was quiet.

　　Note:

　　① before除了可表示 “在…之前”外，还可用来强调主句所表达的时间、距离很长或花费的力量相比较大，可译为“…才”。(“not … before” 可用来强调主句所表达的时间、距离很短或花费的力量相比较小，可译为“…就”)。

　　It was a long time before I got to sleep again.

　　They had not been married a month before they quarreled.

　　② 如果位于when引导的分句之前的主句使用过去进行时、过去完成时或“was/were about to, was/were on the point of”等结构时，when表示突然发生某事，可译为“正在…突然”或“刚…就”等。这时，不能够用as或while来代替when。

　　I was walking on the street when I ran into my old friend John.

　　She had just fallen asleep when the telephone rang.

　　We were about to leave when it began to rain.

　　2) 条件状语从句

　　条件状语从句主要由以下连词引导：if, unless, providing/provided (that), suppose/supposing (that), on condition (that), as/so long as, in case等。

　　So long as you work hard, you will surely achieve good results in examinations.

　　I shall return next Thursday unless something unexpected happens.

　　I will go provided that you go with me.

　　Please give this letter to John in case he comes.

　　3) 让步状语从句

　　让步状语从句主要由以下连词引导：though, although, even if, even though, whatever, however, whoever, wherever, no matter how/ what/ where/ when等。以下介绍几种较特殊的让步状语从句。

　　(1) while引导的让步状语从句多放在句首，while相当于although，表示“尽管”，“虽然”。

　　While I admit I did it, I didn’t intend to.

　　While I understand what you say, I can’t agree with you.

　　(2) 短语“even now/then/so”相当于“though it is/was true”，表示“尽管如此”，“尽管这样”。

　　The fire was out, but even so, the smell of smoke was strong.

　　I’ve tried my best, but even now/then she is not satisfied.

　　(3) as引导的让步状语从句要倒装。

　　Child as he was, he could speak four languages.

　　Hard as she tried, she failed to get the job.