1、常用連詞的用法辨析while, when, as這三個連詞都可引導時間狀語從句，但用法有所不同。1）當某事正在進行的時候，又發(fā)生了另一件事。While, when, as都可用來 引導表示“背景”的時間狀語從句。例如：A/When/While I was walking down the street I noticed a police car.2）當兩個長動作同時進行的時候，最常用的是while。例如：While mother was cooking lunch, I was doing my homework.3）當兩個動作都表示開展變化的情況時，最常用的是例如：As children

2、get older, they become more and more interested in things around them.4）當兩個短動作同時發(fā)生時，或表示“一邊一邊”時，最常用as。例如： Just as he caught the fly, he gave a loud cry.She looked behind from time to time as she went5）當從句的動作先于主句的動作時，通常用when。例如：When he finished his work, he took a short rest.6）當從句是瞬間動作，主句是延續(xù)性動作時，通常用wh

3、eno例如：When John arrived I was cooking lunch.as, because, since , for這四個詞都可表原因，但用法有區(qū)別。1）如果原因構成句子的最主要局部，一般用because。因此，because引導 的從句往往放在句末。例如：stayed at home because it rained.一Why arent you going?-Because I dont want to.2）如果原因已被人們所知，或不如句子的其它局部重要，就用as或since。 Since比as稍微正式一點。As和since引導的從句一般放在句子的開頭。 例如：As

4、he wasnt ready, we left without him.Since I have no money, I cant buy any food.for用來補充說明一種理由，因此，for引導的從句幾乎可以放在括號里。 For引導的句子不放在句子的開頭。例如：I decided to stop and have lunchfor I was feeling quite hungry.if, whetherif和whether都可作“是否”講，在引導賓與從句是一般可互換。例如：I wonder whether (if) you still study in that school.I

5、dont know whether (if) he likes that film.在以下情況下，只能用whether,不能用if：1)引導主語從句時。例如：Whether he will come to the party is unknown.2)引導表語從句時。例如：The question is whether 1 can pass the exam.3)在不定式前。例如：I havent made up my mind whether to go there or not.so.that, such.thatothat中的so是個副詞，其后只能跟形容詞或副詞,而such.that中

6、的such是個形容詞，后接名詞或名詞短語。例如：Im so tired that I cant walk any farther.It was such a warm day that he went swimming.2)如果在名詞之前有many, much, little, few時,用so,不用sucho例如： He has so little education that he is unable to get a job.I have had so many falls that 1 am black and blue all over.either.or., neither.nor

7、, not only.but also.這三個連詞詞組都可連接兩個并列成分。當它們連接兩個并列主語時， 謂語動詞要隨相鄰的主語變化。例如：Either you or he is wrong.Neither he nor his children like fish.Not only the teacher but also the students want to buy the book.although, but這兩個連詞不能用在同一個句子中。例如：我們不能說“Although he is over sixty, but he works as hard as others.”這個句子應改為：Although he is over sixty, he works as hard as others或 He is over sixty, but he works as hard as others.because, so這兩個連詞同樣不能用在同一個句子中。例如：我們不能說“Because Johnwas ill, so I too