是一种在句子与句子之间，短语之间以及名词等其他词语之间起连接作用的虚词，它不能单独作句子的成份。按其意义可分为并列连词和从属连词两大类。

常有的并列连词有

and, both…and, either…or, neither…nor， not only…but also, as well as等。但如果连接的两部分意义不趋向一致，：but, however, yet, still，while等。Mary was a nice girl, but she had one shortcoming.

Tomgot up early, yet he failed to catch the train.

He was very tired, still he kept on walking.

Your composition is fairly good, however, there is still some room for improvement.

还有表示选择关系的并列连词

Jane is hard working ,while her sister is quite lazy.如：or, or else, otherwise… 再有的是连接双方，互为因果，或表示前因后果的连词有：for, so, therefore (因此)，then等。如：that, if, whether, 其次用来连接状语从句。：when , while, as, since, before, after, once, as soon as, until, till。if, unless, as long as 等，because, since, as, now that (既然)。so that, so…that, such…that, as…as, than, where… 它们在句子与文章中几乎无处不见。too...to...意为“太……以至于不能……”,与so...that...结构互换时,that从句中必须使用情态动词can't(如果是过去时则用couldn't)。如:Hewassocleverthathecouldn'tmakesuchstupidmistakes.→ Hewastooclevertomakesuchstupidmistakes.他太聪明了,不会犯这么愚蠢的错误。

温馨提示:如果主从句的主语不一致,改为同义句时,要用too...for sb. to...结构。如:ThatquestionissodifficultthatIcan'tworkitout.→Thatquestionistoodifficultformetoworkout.这个问题太难,我算不出来。

B. 与enoughtodo/notenoughtodo结构的转换

enough to do sth.意为“……足够做某事”,与so...that...结构转换时,that从句中必须使用情态动词can。如:Youaresohealthythatyoucangetbacktoschool.→ Youarehealthyenoughtogetbacktoschool.你身体健康,可以回学校去了。not...enough to do意为“没到做某事的……”,与so...that...结构转换时,that从句中必须使用含有否定意义的情态动词。enough前面的形容词是so...that...结构中so后面形容词的反义词。如:Theboyissoyoungthathecan'tdresshimself.→Theboyisnotoldenoughtodresshimself.这个孩子还没到自己穿衣服的年龄。Heissoimpatientthathecan'twait.→ Heisnotpatientenoughtowait.

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