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专题八 状语从句、定语从句状语从句一、时间状语从句1．before 引导的从句中不用否定式谓语。
常用如下句型： It is long before...(过了好久才……) It is not long before...(过了不久就……)2．since 后面所用动词不同，该动词所表示动作持续时间的计算方法也不同。
⎩⎪⎨⎪⎧since ＋瞬间动词过去式从该动作发生时算起since ＋持续性动词过去式从动作结束时算起It is two years since he joined the army. It is two years since he smoked. 二、地点状语从句多由where 和wherever 引导。
Where there is a will ，there is a way. 二、原因状语从句在表示原因时，because 语气最重，其次是as ，since ，now that ，故在回答why 问句或者在强调句对原因进行强调时，只能用because 。
for 是并列连词，表示推测的理由或者进一步说明，不能放在句首，for 前要用逗号。
—Why were you absent? —Because I was ill. 三、目的状语从句1．so that/in order that 引导的目的状语从句中的谓语动词多用can/could/may/might/will/would ＋动词。
Please turn off the light so that I can go to sleep. 2．for fear that ，in case ，lest 表示“以防，免得”。
He is working hard for fear that he should fail. 四、条件状语从句1．providing/provided (that)假如，假若Providing (that) no one has further questions ，the meeting will be over. 2．on the understanding that ＝on condition that 在……条件下I give you money on the understanding that you finish your homework.五、结果状语从句注意such 引导的结果状语从句与定语从句的区别。
状语从句由从句担任的状语，在句子中可修饰谓语（或其它动词）、形容词、副词或是整个句子，它可以用来表示时间、地点、原因、目的、结果、条件、方式、比较、让步等。
第一讲时间, 地点状语从句时间状语从句：when, while, as, before, after, since , wheneveruntil, till, by the time(注意时态)as soon as, had hardly…when, had no sooner…than, (on doing sth…)the moment, every time/ each time, the first time, oncee.g: When he came, I had cleaned the classroom.He didn’t stop working until his mother came bake.He worked until his mother came back.As soon as he returned, he bought a new flat.He had no sooner returned than he bought a new flatHe came to scene the moment he heard the news.I thought her nice and honest the first time I met him.Once he makes up your mind, he won’t change his min d.It was two years before I met him again. = Two years passed before I met him again.注意点1. when引导的从句动词可以是延续性的或短暂性的，while引导的从句中动词必须是延续性的；while有时并不表示时间，而表示对比，表示“而”、“却”。
