20.5 表原因关系 1) for 判断改错： 　 (错) For he is ill, he is absent today. 　 (对) He is absent today, for he is ill. 　 for是并列连词，不能置于含两个并列分句的句子的句首，只能将其放在两个分句中间。 2) so, therefore 　He hurt his leg, so he couldn't play in the game. 注意： 　 a. 两个并列连词不能连用，但therefore, then, yet.可以和并列连词连用。 　　You can watch TV, and or you can go to bed. 　　He hurt his leg, and so / and therefore he couldn't play in the game. 　 b. although… yet…，但although不与 but连用。 　 (错)　Although he was weak, but he tried his best to do the work.. 　 (对)　Although he was weak, yet he tried his best to do the work.

20.4 表示转折或对比 　1) but表示转折，while表示对比。 　 Some people love cats, while others hate them. 典型例题　 --- Would you like to come to dinner tonight?　 --- I'd like to, ___ I'm too busy. 　A. and　 B. so　 C. as　 D. but　 　答案D。but与前面形成转折，符合语意。而表并列的and， 结果的so，原因的as都不符合句意。 　2) not…but… 意思为"不是……而是……" 　 not 和but 后面的用词要遵循一致原则。 　 They were not the bones of an animal, but (the bones) of a human being.

20.2 比较and和or 　1) 并列结构中，or通常用于否定句，and用于肯定句。 　2) 但有时and 也可用于否定句。请注意其不同特点： 　 There is no air or water in the moon. 　 There is no air and no water on the moon. 　在否定中并列结构用or 连接，但含有两个否定词的句子实际被看作是肯定结构，因此要用and。 典型例题 　---I don't like chicken ___ fish.　 　---I don't like chicken, ___ I like fish very much. 　A. and； and　 B. and； but　C. or； but　D. or；and 　答案C。否定句中表并列用or, but 表转折。 判断改错： 　(错) We will die without air and water. 　(错) We can't live without air or water. 　(对) We will die without air or water. 　(对) We can't live without air and water. 20.3 表示选择的并列结构

　1) or　意思为"否则"。 　 I must work hard, or I'll fail in the exam. 　2) either…or　意思为"或者……或者……"。注意谓语动词采用就近原则。 　 Either you or I am right.

20.1 并列连词与并列结构 　并列连词引导两个并列的句子。 1)　and 与or 　判断改错： 　(错) They sat down and talk about something. 　(错) They started to dance and sang. 　(错) I saw two men sitting behind and whisper there. 　(对) They sat down and talked about something. 　(对) They started to dance and sing. 　(对)I saw two men sitting behind and whispering there. 解析： 　 第一句： and 连接两个并列的谓语，所以 talk 应改为 talked。 　 第二句：and 连接两个并列的动词不定式，第二个不定式往往省略to，因此sang 应改为 sing。 　 第三句：and 连接感观动词saw 后面的用作的宾补的两个并列分词结构，因此whisper应改为whispering。 注意：and 还可以和祈使句或名词词组连用表示条件。(or也有此用法) 　 Make up your mind, and you'll get the chance. 　 = If you make up your mind, you'll get the chance. 　 One more effort, and you'll succeed. 　 = If you make one more effort, you'll succeed. 2)　both …and　两者都 　She plays (both) the piano and the guitar. 3)　not only…but (also), as well as不但…而且) 　　She plays not only the piano, but (also) the guitar. 　 注意： not only… but also 关联两个分句时，一个分句因有否定词not 而必须倒装。 　 Not only does he like reading stories, but also he can even write some. 　4)　neithe…nor 意思为"既不……也不……"谓语动词采用就近原则，与nor后的词保持一致。 　　Neither you nor he is to blame.

19.10 表示"一…就…"的结构 　hardly/scarcely…when/before, no sooner…than　和as soon as都可以表示"一…就…"的意思，例： 　I had hardly / scarcely got home when it began to rain. 　I had no sooner got home than it began to rain. 　As soon as I got home, it began to rain. 　注意：如果hardly, scarcely 或no sooner置于句首，句子必须用倒装结构： 　Hardly / Scarcely had I got home when it began to rain. 　No sooner had I got home than it began to rain. 连词

19.9 比较until和till

此两个连词意义相同。肯定形式表示的意思是"做某事直至某时"，动词必须是延续性的。否定形式表达的意思是"直至某时才做某事"。动词为延续性或非延续性都可　以。 正确使用这两个连词的关键之一就在于判断句中的动词该用肯定式还是否定式。 　 　 肯定句： 　 I slept until midnight. 我一直睡到半夜时醒了。 　 Wait till I call you.　 等着我叫你。 　 (在肯定句中可用before代替 Let's get in the wheat before the sun sets.) 　 　 否定句： 　 She didn't arrive until 6 o'clock. 　 她直到6点才到。 　 Don't get off the bus until it has stopped. 　 公共汽车停稳后再下车。 　 I didn't manage to do it until you had explained how.　 直到你教我后，我才会做。 1)Until可用于句首，而till通常不用于句首。 　Until you told me, I had heard nothing of what happened. 　直到你告诉我以前，出了什么事我一点也不知道。　 2)Until when 疑问句中，until要放在句首。 　 ---Until when are you staying?　你呆到什么时候？ 　 --- Until next Monday.　呆到下周一。　 注意：否定句可用另外两种句式表示。 (1)Not until …在句首，主句用倒装。 　Not until the early years of the 19th century did man know what heat is. 　直到19 世纪初，人类才知道热能是什么。 　Not until I began to work did I realize how much time I had wasted. 　 直到我开始工作，我才认识到了我已蹉跎了几多岁月。 (2)　It is not until… that…

19.8 比较while, when, as 1)as, when 引导短暂性动作的动词。 　　 Just as / Just when / When I stopped my car, a man came up to me. 2)当从句的动作发生于主句动作之前，只能用when 引导这个从句，不可用as 或 while。 　　 When you have finished your work, you may have a rest. 3)从句表示"随时间推移"连词能用as，不用when 或while。 　　 As the day went on, the weather got worse.　 　　日子一天天过去，天气越变越坏。

19.7 让步状语从句 though, although 　注意： 当有though, although时，后面的从句不能有but，但是 though 和yet可连用 　Although it's raining, they are still working in the field.　 　虽然在下雨，但他们仍在地里干活。 　He is very old, but he still works very hard.　 　虽然他很老，但仍然努力地工作。 　Though the sore be healed, yet a scar may remain. 　伤口虽愈合，但伤疤留下了。 (谚语) 典型例题 1) ___she is young, she knows quite a lot.　 A. When　B. However　 C. Although　 D. Unless 答案：C。意为虽然她很年轻，却知道许多。 2)　as, though 引导的倒装句 　 as / though引导的让步从句必须表语或状语提前(形容词、副词、分词、实义动词提前)。 　Child as /though he was, he knew what was the right thing to do. 　= Though he was a small child, he knew what was the right thing to do. 注意： a.　句首名词不能带任何冠词。 　　b.　句首是实义动词，其他助动词放在主语后。如果实义动词有宾语和状语，随实义动词一起放在主语之前。 　 Try hard as he will, he never seems able to do the work satisfactorily. 　 = Though he tries hard, he never seems… 　虽然他尽了努力，但他的工作总做的不尽人意。 3)　ever if, even though.　即使 　We'll make a trip even though the weather is bad. 4) whether…or-　 不管……都 　 Whether you believe it or not, it is true. 5)　"no matter +疑问词" 或"疑问词+后缀ever" 　 No matter what happened, he would not mind. 　 Whatever happened, he would not mind. 　 替换：no matter what = whatever 　　 no matter who = whoever 　　 no matter when = whenever 　　 no matter where = wherever 　　 no matter which = whichever 　　 no matter how = however 　 注意：no matter 不能引导主语从句和宾语从句。 　(错)No matter what you say is of no use now. 　(对)Whatever you say is of no use now. 　　 你现在说什么也没用了。(Whatever you say是主语从句) 　(错)Prisoners have to eat no matter what they're given, 　(对)Prisoners have to eat whatever they're given.　囚犯们只能给什么吃什么。

19.6 条件状语从句 　连接词主要有 if, unless, as/so long as, on condition that 等。. 　if 引导的条件句有真实条件句和非真实条件句两种。非真实条件句已在虚拟语气中阐述。 　 unless = if not.　 　 Let's go out for a walk unless you are too tired. 　 If you are not too tied, let's go out for a walk. 典型例题 You will be late ___ you leave immediately.　 A. unless　 B. until　 C. if　D. or 　答案A。 句意：除非你立即走，否则你就回迟到的。可转化为 If you dong leave immediately, you will be late.　B、D句意不对，or表转折，句子如为 You leave immediately or you will be late.

19.5 结果状语从句 　结果状语从句常由so… that 或 such…that引导，掌握这两个句型，首先要了解so 和 such与其后的词的搭配规律。 比较：so和 such 　其规律由so与such的不同词性决定。such 是形容词，修饰名词或名词词组，so 是副词，只能修饰形容词或副词。 so 还可与表示数量的形容词many, few, much, little连用，形成固定搭配。 　so foolish　　　　such a fool　　　　 　so nice a flower　　such a nice flower　 　 　so many / few flowers　 such nice flowers　　 　so much / little money. such rapid progress　　 　so many people　　　such a lot of people　 　 ( so many 已成固定搭配，a lot of 虽相当于 many，但 a lot of 为名词性的，只能用such搭配。) 　 so…that与such…that之间的转换既为 so与such之间的转换。 　 The boy is so young that he can't go to school. 　 He is such a young boy that he can't go to school