从属连词用来连接各种从句。until(till)直到,在用until表达时间状语的句子中,主句中的动词是要十分小心去选择的。如动词是持续性动词,它要用肯定句,如:I studied hard until 12 o'clock last night.如果动词是瞬间截止性动词,则要用否定句,如:He didn't go to bed until his mother came back.由since,for,by,before, 来引导的时间状语从句。since 引导的时间状语是动作的开始时间,如:I have studied English since 1990.而by引导的时间状语通常是动作的结束时间,如:I had learned 25 English songs by the end of last term.上述连词的用法,看起来不难,但错误也难免。下面是些好例子:(1) This book may be used both as a text as well as a reference book.这里的“as well as”和“both”不能搭配,应该将“as well as ”改为“and”,使“both.......and......”变成关联连词( correlative conjunction)(2) He not only speaks Mandarin but also English.这里的“not only”应该移到“speaks”后面,使这个动词兼顾两个独立宾语:“Mandarin”和“English”。(3) Although he is fat, but he is very weak.英语里的“although”和“but”是不见面的 ,因此这句里的“ but”要去掉,不然“although”就要去掉。(4) Jim is not so strong like you.这里的“not so”必须和“as”连成一体;介词“like”是不适宜的。(5) No sooner had we reached our destination, they left."No sooner"必须和"than" 配成关联连词,把"than" 省掉是不对的,应该补上:No sooner had we reached our destination than they left.这句子的意思也可透过“as soon as”反映出来:“As soon as we reached our destination, they left.”(6) I took a taxi and which took me to the station.这里的并列连词“and”是多余的,必须去掉。如果要保留“and ”也可,但是形容词分句里的关系代词“Which”要改成主语“it” ,使整个句子变成并列分句如下:I took a taxi and it took me to the station.(7) My friend came up to me and held my hand, said good-bye excitedly.这里的“and”应该用来连接最后两个谓语才对:My friend came up to me, held my hand, and said good-bye excitedly.不然,就要把“said”改成“saying”。“saying”起主要作用。