当as意为由于,在句中是原因状语从句时,as前为主句,还是as后为主句?

当as意为由于,在句中是原因状语从句时,as前为主句,还是as后为主句?

1）引导时间状语从句 ①在as引导的时间状语从句中,谓语动词既可以是延续性的也可以是非延续性的；有时从句的谓语动词也可用进行时形式.②as引导的时间状语从句常可用来强调主、从句中的动作同时发生或伴随发生,常译作“随着„„”,“一边„„一边„„”,“一„„就„„”等.③在省略句中,as之后经常放置一个名词或名词词组. I heard the murmur of their voices as I crossed the hall. A look of surprise came into Alison’s eyes as she read the message. Scott became nervous as he saw her face. Just as he was speaking there was a loud explosion. He smiled as he passed. As she sang,the tears ran down her cheeks. We get wiser as we get older. As a young man,he was a store keeper and later a postmaster. 2）引导让步状语从句 象although,though,while一样,as也可以用来引导一个让步状语从句,意为“尽管,虽然”, as引导的这种让步状语从句语气比较强,语体正规,经常用于书面语言,但as引导的让步状语从句须倒装.其倒装要求如下： ①表语＋as＋主语＋系动词 （表语经常是由形容词、分词、或名词充当；名词用作表语时,其前不能加用冠词.） Young as he is,he is equal to the task. Crowded as the restaurant was,they tried to find a table. Child as he was,he knew what was the right thing to do. ②状语﹢as﹢主语﹢谓语动词 （这一结构中的谓语动词一般是行为动词,既可以是及物动词（带宾语）也可以是不及物动词.） Hard as he studied,he did not get good marks in the exam. Early as we got there,our teacher was there before us. Much as I admire him as a writer I don’t like him as a man. ③动词＋as＋主语＋…… （在这一结构中,主语后面一般加上情态动词may,might,will,would,can,could等,句首的动词应该保持原形.如果从句中没有情态动词,那么,应在从句的主语之后（根据时态和数的要求）加上助动词do、does或did.在这一结构中,放在句首的动词如果是及物动词,那么,这个动词连同它的宾语一起放到as之前.） Search as they would,they could find nothing in the house. Try as he may,he will fail in the examination. Die as he did,his inspiration lived on. Lose money as I did,I got a lot of experience. 3）引导原因状语从句 as引导原因状语从句时,语气不及because强烈,它接近于since,now that,一般译作“既然,由于”之类的意义,只是“附带说明的理由”,表达一种说话人和听话人“共知的原因”.as引导的原因状语从句一般置于主句之前. As all the seats were full he stood up. As Davidson had a passion for walking,we started off on foot. As you are sorry,I’ll forgive you. It is very difficult for us to know what to do as we are not his parents. 4）引导方式状语从句 as引导方式状语从句时,只修饰和说明主句的谓语动词,表示“按照,依照”、“用什某么方式或方法”；as只起引导词的作用,一般不在从句中充担成分；从句一般应置于主句之后,有时也可置于主句之前. She cooks fish as my mother does. We must do as the Party tells us to. We should learn a foreign language as Marx did. As you like maths,I like biology. As a man lives,so he dies. When at Rome do as the Romans do. 5）引导表语从句 as有时可以用来引导一个表语从句,意为“像„„的样子（那样）”. Things were almost as they had been before. His rooms were exactly as he had left them. The cottage is just as it was in Shakespeare’s time. ▲有时可以用来表示比例关系：2 is to 4 as 8 is to 16.（2﹕4 ﹦8 ﹕16） 6）引导比较状语从句 as可以构成“as „ as „”结构,表示“原级比较”或“加强语气”,意为“象 „„ 一样”、“„„ 达”.在这一结构中,第二个as引导的是一个比较状语从句.这一从句经常使用省略句. You know as much about that as I do. I haven’t done as much as I should have liked. Martin was as impatient as he was stubborn. He considered her opinion as valuable as any of ours. Waves of red light are about twice as long as waves of blue light. She can run as fast as 20 miles an hour. The newly-built bridge is as long as 800 meters. 7）引导补充说明性从句 在leave „ as they / it be 句型中,as引导的是一个补充说明性从句,具有宾语从句的作用.本句型意为“使 „„ 处于原有状态”.注意前后时态的呼应和数的一致. Please leave things as they are. We left all the books as they were. We should leave nature as it is. 8）引导限制性定语从句 若限制性定语从句的先行词接受the same 或such修饰时,我们通常要使用as 来引导定语从句,as在从句中可以充当主语、宾语或表语.定语从句可以是一个省略句. Such women as knew Tom （Those women who knew Tom）thought he was charming. I never heard such stories as he tells. We drove out of the town by the same road as we had entered by. Robbie looked just the same as ever. 3 We are now in the same position as at the end of last summer. 9）引导非限制性定语从句 as 引导非限制性定语从句时,意为“象 „„ 一样”, 定语从句不修饰限制具体的引导词,而是对整个主句或主句中的某一部分进行概括性说明或评价,表明说话人对话语内容的的态度,as在从句中可以充当主语、宾语或表语.as引导的非限制性定语从句可以置于主句之前、插入到主句之中,也可以放在主句之后,还可以使用省略句. As is known to us all,the population of China is much larger than that of the United States. As was expected,he performed the task with success. As we all know,heavy objects and light objects fall at the same speed unless air holds them back. As we have seen,oceans cover more than 70 percent of the surface of the earth. The elephant is like a snake,as anybody can see. The problem is not easy to solve,as indeed it is. Mary was late again,as（ had been） expected. ●as引导的非限制性定语从句经常说明说话人的态度、依据、评论,有逗号与主句隔开,有时也可与which 换用.然而,as引导的非限制性定语从句总有“象 „„ 一样”的含义,而which则没有这样的含义. which 常译作“这一点”、“那一点”、“这一情况”等类似的语义.具有概括性含义. which 引导的非限制性定语从句,可以修饰限制主句中的某一个名词或代词（有具体的先行词）,也可以修饰说明整个主句或主句中的某一部分.which引导的从句一般置于主句之后或置于被修饰限制的部分之后,但不可置于主句之前.which常在从句中作主语、宾语、表语或定语等成分.which引导的非限制性定语从句常说明一种情况、状况或结果,有逗号与主句隔开. as Mary,as we all know, is a clever girl. He didn't come on time, as （could be）expected. As anybody can see, great changes have taken place in our country. He opposed this idea,as （could be） expected. which They have visited me in hospital,which is very kind of them. They （all kinds of bamboo）are hollow,which makes them very light. The little girl spoke very good English,which surprised all of us. It rained hard,which prevented me going out. The Blacks invited me to dinner, which / as was very kind of them. The child was from Baoding,as /which they knew from his accent