是一種在句子與句子之間，短語之間以及名詞等其他詞語之間起連接作用的虛詞，它不能單獨作句子的成份。按其意義可分為并列連詞和從屬連詞兩大類。

常有的并列連詞有

and, both…and, either…or, neither…nor， not only…but also, as well as等。但如果連接的兩部分意義不趨向一致，：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.

還有表示選擇關系的并列連詞

Jane is hard working ,while her sister is quite lazy.如：or, or else, otherwise… 再有的是連接雙方，互為因果，或表示前因后果的連詞有：for, so, therefore (因此)，then等。如：that, if, whether, 其次用來連接狀語從句。：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… 它們在句子與文章中幾乎無處不見。too...to...意為“太……以至于不能……”,與so...that...結構互換時,that從句中必須使用情態動詞can't(如果是過去時則用couldn't)。如:Hewassocleverthathecouldn'tmakesuchstupidmistakes.→ Hewastooclevertomakesuchstupidmistakes.他太聰明了,不會犯這么愚蠢的錯誤。

溫馨提示:如果主從句的主語不一致,改為同義句時,要用too...for sb. to...結構。如:ThatquestionissodifficultthatIcan'tworkitout.→Thatquestionistoodifficultformetoworkout.這個問題太難,我算不出來。

B. 與enoughtodo/notenoughtodo結構的轉換

enough to do sth.意為“……足夠做某事”,與so...that...結構轉換時,that從句中必須使用情態動詞can。如:Youaresohealthythatyoucangetbacktoschool.→ Youarehealthyenoughtogetbacktoschool.你身體健康,可以回學校去了。not...enough to do意為“沒到做某事的……”,與so...that...結構轉換時,that從句中必須使用含有否定意義的情態動詞。enough前面的形容詞是so...that...結構中so后面形容詞的反義詞。如:Theboyissoyoungthathecan'tdresshimself.→Theboyisnotoldenoughtodresshimself.這個孩子還沒到自己穿衣服的年齡。Heissoimpatientthathecan'twait.→ Heisnotpatientenoughtowait.

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