e 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…"，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. 这些不是动物的骨头，而是人的。

20.5 表原因关系
1） 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。
判断改错：（错） For he is ill, he is absent today.
　 （对） He is absent today, for he is ill.
2） so为连词, therefore一般为副词。例如：
He hurt his leg, so he couldn't play in the game. 他的腿受伤了，不能上场。
I think; therefore I exist. 我思故我在。

20.6 比较so和 such
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 + adj.　　　　　　　　　 such + a（n） + n.
so + adj. + a（n） + n.　　　 such + n. （pl.）
so + adj. + n. （pl.）　　　 such +n. （pl.）　
so + adj. + n. （不可数）　　such +n.（不可数）
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之间的转换即为 so与such之间的转换。
20.7 连词和从句练习
1. 1. I’d get it for you ______ I could remember who last borrowed the book.
a. on condition that b. now that c. except that d. considering that
2. 2. The robber told him that he had better keep silent ______ he wanted to get into trouble
a. if b. unless c. otherwise d. whether
3. 3. Strange ______ his behavior may be, there is a very good reason for it.
a. although b. even if c. that d. as
4. 4. We are worried about our son because no one is aware ______ he has gone.
a. the place b. of where c. about the place d. where
5. 5. The professor spoke in a loud voice ______ every one of us could hear him.
a. such that b. so c. so that d. such
6. 6. When he just got off the plane, he gave us a good description of ______ in Spain.
a. what he had seen b. that he had seen c. which he had seen d. he had seen what
7. 7. It is fitted with a small transformer, by means of ______ the voltage of the currency can be adjusted.
a. whom b. which c. what d. that
8. 8. I don’t know why she’s looking at me ______ she knew me. I’ve never seen her before in my life.
a. as b. although c. even if d. as if
9. 9. No sooner had he finished his speech ______ stormy applause broke out.
a. when b. then c. than d. as
10. 10. It is hard to avoid mistakes. ______ you correct them conscientiously, it will be all right.
a. In the case b. As long as c. Although d. Despite
11. 11. Geometry, ______ I know nothing, seems a very dull subject.◆本◆作◆品◆由◆◆網◆友◆整◆理◆上◆傳◆
a. that b. about that c. which d. about which
12. 12. The highest temperature ______ in any furnace on earth is about 10,000 centigrade.
a. we can get b. that we can get it c. which we can get it d. what we can get
13. 13. We sent the horses to a considerable distance, ______ they should disturb the children.
a. less b. lest c. last d. least
14. 14. Sound is conducted through steel in the same manner ______.
a. as in air b. as through air c. as air does d. like air
15. 15. _____ he was putting on his uniform, the officer found that one of the sleeves was torn.
a. Since b. Unless c. As d. Before
16. 16. The police finally caught up with the man ______ was the escaped prisoner.
a. who they thought b. whom they thought
c. they thought him d. that they thought him
17. 17. ______ knows the name of this song will receive a prize from the radio station.
a. Whoever b. Those c. Whichever people d. Any people
18. 18. ______ do you believe is not about to support our plan?
a. Whom b. Who c. Whomever d. Which
19. 19. He didn’t know French, ______ made it difficult for him to study at a university in France.
a. that b. as c. this d. which
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