2．On the arrival of Tom’s birthday,he was________anxious________get a gift from Mary. A．very;for
B．too;for C．too;to
D．enough;to 解析：选C.句意：汤姆的生日到了,他非常想从玛丽那里得到一份礼物.选项A和B的介词for后应用getting;D项的enough应放在anxious之后.选C. 温馨提示 请做课时作业 必修三 Unit 8 本部分内容讲解结束 按ESC键退出全屏播放 跟踪训练 Ⅰ.选词填空 take off，right now，in order to，get across，turn up，break down 1．He got up very early this morning________________catch the first bus. in order to 2．She________________my wet boots and made me sit by the fire. 3．He’s not in the office________________. 4．Your meaning didn’t really________________. took off right now get across 5．Our car___________on the freeway. 6．We arranged to meet at 8∶00,but she never___________.
broke down turned up Ⅱ.单项填空 1．How can you________and do nothing while I am in great trouble? A．stand for
B．stand by C．stand out
D．stand up 解析：选B.考查stand构成的短语辨析.句意：在我有大麻烦的时候,你怎么可以袖手旁观,什么都不做呢？stand for代表,拥护;stand by坚持某种说法,袖手旁观,支持;stand out 突出,显眼,杰出;stand up站立,起立.故选B. 2．—How about your journey to Mount Emei? —Everything was wonderful except that our car________twice on the way. A．slowed down
B．broke down C．got down
D．put down 解析：选B.考查动词短语辨析.句意：——你们去峨眉山的旅行怎么样？——除了我们的车在路上坏了两次以外,其他一切都很好.break down抛锚;垮掉,符合题意.slow down减慢;get down写下;put down写下;放下。 3．—Time is running out.We’d better hurry up,or we’ll miss the deadline. —Don’t worry.We have already________80% of the job. A．got through
B．got across C．looked through
D．passed through 解析：选A.考查短语辨析.get through穿过,完成,符合题意.get across被理解;look through仔细检查,看穿;pass through经历,经过,通过. 4．She didn’t go because she didn’t want to________seeing Neil again. A．at the risk of
B．run the risk of C．take a risk
D．risk of 解析：选B.本题考查固定搭配.“冒险做某事”用take/run the risk of doing sth.或risk doing sth.,故答案为B. 5．________sunshine and some rainfall promise a good harvest of fruits and vegetables this year. A．A large quantity of
B．Large quantities of C．A large number of
D．A good many 解析：选B.考查词语辨析.因sunshine和rainfall为不可数名词,故排除C、D项.并且谓语动词promise为复数故排除A项.
6．The painting appears very beautiful if you look at it________. A．in the distance
B．at a distance C．in a long way
D．from the distance 解析：选B.本题考查词组辨析.句意：如果从一定距离看这幅画,看起来很美.“从一定距离”,用at a distance或from a distance;而in the distance意为“在远 处”,故答案为B. 7．—You promised to help—you mustn’t________now. —No,I won’t. A．pick out
B．back out C．make out
D．take out 解析：选B.考查动词短语辨析.句意：——你答应帮忙了,你决不能不履行诺言.——不,我不会不履行的.pick out “挑出”;back out “决定不履行(允诺的事)”; make out “辨认出,了解”;take out “带出去”.故选B. 句型巧析 1(教材P26)Marco was surprised to see_Chinese_people_using paper money in the markets. 马可很惊讶地看到中国人在集市上使用纸币. 【句法分析】句中see sb. doing sth.意为“看见某人正在做某事.”在see，hear, find，watch，notice，observe等感官动词之后既可跟现在分词作宾语补足语，又可跟省略to的不定式作宾语补足语(但在被动语态中不能省略to)，还可跟过去分词作宾语补足语。 ①I hate to see you leave so soon. 我真不想让你这么快就离开. ②At dusk,I found_him_crying in the street. 黄昏时,我发现他在街上哭. ③I heard_her_playing the piano in the next room. 我听见她在隔壁弹钢琴.
2(教材P26)Although people enjoyed reading his book,many of them thought that Marco’s stories about China were too fantastic to be true. 尽管人们爱读他的书,但许多人认为马可写的有关中国的故事太离奇而不可信. 【句法分析】(1)该句中使用了too...to...结构，意为“太……而不能……”，too后面跟形容词(或副词)，但当其后接形容词修饰单数可数名词时，要把不定冠词a(n)放在形容词之后。 (2)too...to...句式中,若too后接glad,pleased,happy, eager,anxious,willing,ready,easy 等表示心情、情绪等的形容词，表示肯定意义，too相当于very。,(3)如果too前有否定词never或not(即never/not too...to...)，或者不定式前有not(即too...not to do...)时，这两种形式均表示肯定意义。 ①It was too hot a day for us to work. 天太热了,我们不能干活. ②He is too_weak_to_carry the box. ＝He isn’t strong enough to carry the box.＝He is so weak that he can’t carry the box. 他太弱了,搬不动这个箱子. ③They seemed to be too nervous and were too anxious to_leave.他们看起来非常紧张,并且急于离开.
跟踪训练 Ⅰ.完成句子 1．原来你在这儿!我到处都把你找遍了. ___________________!I’ve been looking for you everywhere. There you are 2．有人看见他带走了那本书. He______________________take away that book. 3．人们一个一个地离开了. _______________________one by one. was seen to Away went the crowd 4．当我们到那里时,看到她在和邻居聊天. When we arrived there, we________________________her neighbors. saw her chatting with Ⅱ.单项填空 1．He looked around and saw a man________his hand into the pocket of a passenger. A．put
B．to be putting C．to put
D．putting 解析：选D.考查“see＋宾语＋宾语补足语”的结构.省略to的不定式作宾语补足语,表示“a man”与“put”之间为主动关系,且表示动作的全过程;现在分词作宾语补足语,表示主动关系且动作正在进行;过去分词作宾语补足语表示“a man”与“put”之间为被动关系且动作已完成, 由句意“他向四周看了看,发现一个人正把他的手放进一位乘客的兜里”,可知选D. 短语细解 10take off 脱下(衣,帽,鞋等);起飞;动 身,离开;减去 (教材P116)．..especially when you take_off! ……尤其是当你起飞的时 候! 归纳拓展 ①The prisoner was taken away by an armed guard. 一个持枪的狱警把犯人带走了. ②The salesman finds it easy to take_in old ladies. 这个推销员发现老太太们容易上当受 骗. ③This thing takes_up all my attention. 这件事占据了我所有的注意力. ④In an instant,he took off his coat and jumped into the water.他立刻脱下大衣跳进了水里. 11turn up 出场,到场;开大(音量,水等) (教材P25)When I turned_up for my first jump I was so nervous that I tried to back out,but my friends persuaded me to go through with it. 当我站在台上开始我的第一次跳时,我紧张得真想退出,但我的朋友们说服了我去克服它. 归纳拓展 ①He promised to come at seven,but he has not turned up yet.他答应七点来,但是他还未出现. ②Something unexpected has turned up. 发生了出乎意料的事. ③There was no single person whom she can turn_to in the dark street.在漆黑的大街上没有一个她能够求助的人. ④It turned_out that she was a friend of my sister. 她原来是我姐姐的一个朋友. 辨析
turn,become turn 后接名词作表语时,名词前不用任何冠词. become 后接名词时,名词前要有冠词. 12back out 决定不履行(允诺的事);食言;退出 (教材P25)．..I tried to back_out,but my friends persuaded me to go through with it. ……我试图退出,可我的朋友说服了我去克服它. 归纳拓展 ①The waiter backed away from the table,bowing slightly.这个服务员从桌旁向后退,欠身鞠了个躬. ②When presented with the evidence,the suspect backed_down.拿出证据后,疑犯终于认罪了. ③Once you have given your words,don’t try to back_out. 一旦答应了人家,就不要食言.
13get across 使理解(某事);使明白,表达,通过 (教材P25)It’s difficult to get_across how exciting it is! 很难表达那是多么令人激动!
归纳拓展
助 记
①If everyone keeps in line,we’ll get through the customs more quickly. 如果大家都遵守秩序,我们会很快通过海关. ②She seemed to have got over her distress. 她似乎摆脱了她的悲痛心情. ③I’m going to get_down_to studying English this term. 这学期我要认真学英语了.
辨析
get,gain get 表示“获得”的最普通用语. gain 表示付出更大的努力才能获得,故常意为“赢得”. 14break down 损坏,不能运转;击倒;失败;失去控制;把……分解 (教材P28)First,his two sledges broke_down,and then the horses began to have serious difficulties with the snow and the cold. 先是他的两辆雪橇坏了,后来马匹开始应付不了大雪和严寒的天气. 归纳拓展 ①(2011·高考湖北卷)Mr.McMahon’s daughter broke down—she said you told her he had cancer.麦克马洪先生的女儿要垮掉了——她说你告诉她他得了癌症. ②(牛津P234)The sun broke_through at last in the afternoon.下午太阳终于拨云而出. ③The peace talks are said to have broken_down. 据说和谈破裂了.
④Don’t break in when the adventurer is telling his own story. 当冒险家在讲他自己的经历时,别打断他. ⑤The thief broke off the rope and ran away. 那个小偷挣脱了绳子,逃走了. ⑥The crowd started to break_up when the night fell. 天黑时人群开始散开了.
15run out of 用尽,用光,耗尽 (教材P28)The men were soon exhausted and were running_out_of food. 人们很快就筋疲力尽而且粮食也都用光了.
归纳拓展 辨析 run out,run out of run out 意为“用完,耗尽”,是不及物动词短语.主语通常为时间、食物、金钱等,没有被动形式,但可用于进行时. run out of 意为“将……用光”,是及物动词短语,表示主动含义,主语一般是人. 助 记
①They ran out(of the room)to see what was happening. 他们(从屋里)跑出来看看发生什么事. ②My car has run_out_of petrol,so I can’t start it. 我的车没汽油了,所以发动不了. 【重点提示】 run out 为不及物动词短语,主语一般为物,以主动形式表示被动意义;run out of为及物动词短语,接宾语,其主语一般为人,后接表示时间、精力、钱或物的名词. 16stand by 坚持(某种)说法;站在旁边,袖手旁观;遵守 (教材P26)But Marco always stood_by his tales. 但是马可总是坚持他所讲的故事是真 的.
归纳拓展 ①There were no seats left so I had to stand up. 没有座位了,所以我只好站着. ②Yao Ming stands_out in the crowd. 在人群中姚明很显眼.
①The students are preparing for the final exam. 学生们在为期末考试做准备. ②I was_not_prepared_for all the problems it caused. 我对这事引起的诸多麻烦毫无防备. ③The third book in the series is currently in_preparation. 丛书的第三册现在正准备出版.
8distant adj.远处的;久远的;疏远的,不友好的,冷淡的;远亲的 (教材P28)Later, these rocks proved that at one time in the distant past the Antarctic was covered by plants. 后来,这些石块证实：在远古时代,南极洲地区曾经被植物覆盖.
归纳拓展 ①(2011·高考湖北卷)Hunting grounds are distant and it happens that wolves may separate from one another at times.狩猎场地很远又碰巧狼可能有时是分开的. ②After the quarrel Susan remained cold and distant. 那次争吵之后,苏珊一直非常冷淡疏远. ③What’s the distance from Chicago to Detroit? 芝加哥离底特律有多远？ ④That’s Long Island in_the_distance over there. 那边远处是长岛.
9observe vt.&vi.观察;遵守;庆祝;评述,评论 (教材P30)Air-conditioned vehicles for observing animals. 观察动物的装有空调的交通车辆.
归纳拓展 ①Did you observe anything unusual in his behaviour? 你注意到他的行为有什么不寻常吗？ ②His neighbor observed a stranger enter his house and take away some valuables.他的邻居看见一个陌生人进入他家,拿走了一些贵重物品. ③He was observed to pass by the store in a hurry. 有人发现他从商店旁边匆匆而过.
跟踪训练 Ⅰ.品句填词 1．These children __________ themselves with torches and rope,and then started off. equipped 2．After a month’s fight,the soldiers were all __________ and they were eager to have a good sleep. 3．The young man was born in a __________ family,but he doesn’t think money can buy happiness. exhausted wealthy 4．The mother was __________ about the children when they didn’t come back home from school. 5．There were so many people that the company put on __________ buses. anxious extra 6．The ________(作者)of the book had a lot of difficult experiences in his life. 7．Saunder’s lawyer made a brief __________(陈述)to the press outside the court. author statement 8．The teacher told the students to get ready for a __________(听写)． 9．As a teacher,it is a must for you to have a wide range of knowledge as well as __________(耐心)． 10．The weather in our country ______ (不同)from one place to another. dictation patience differs Ⅱ.单项填空 1．She had thought that he________for the dinner,but in fact he didn’t. A．had prepared B．would have prepared C．prepared
D．would prepare 解析：选B.句意：她本以为他已经准备好了晚餐,但事实上没有.这里是虚拟语气,与过去事实相反时主句用过去完成时,从句用“would have done”.
2．They________each other as to the precise meaning of this article in the contract. A．differ
B．differ with C．differ from
D．differ about 解析：选B.句意：对于合同中这一条款的确切释义他们的看法互不一致.differ with sb.“与某人意见不同”,符合句意.differ from sth.“与……不同”;differ about/on...“在……方面意见不同”;differ 是不及物动词,不能直接跟宾语,故A、C、D三项都不对.
3．Our parents always get a little bit________if we don’t manage to arrive when we say we will. A．eager
B．anxious C．patient
D．earnest 解析：选B.句意：当我们没有在我们所说的时间到达时,我们的父母总是很焦虑的.D项意思为“真诚的”.
4．She’s left a very________message on my answerphone.I can’t understand what she wanted to say. A．confused
B．confusion C．confusing
D．confusedly 解析：选C.句意：她在我的电话答录机上留下了一个含糊不清的留言.我不明白她要说什么.confusing “令人困惑的”,常修饰物,说明物的性质特征.confused指“感到困惑的”,常用来修饰人,说明人的“状态”.故C项正确. 5．I was________with my son about his carelessness,which________the main cause of his failure in maths. A．annoyed;were
B．amazed;was C．amazing;were
D．annoyed;was 解析：选D.考查形容词词义辨析以及定语从句中的主谓一致问题.annoyed“恼怒的,生气的”;amazing “令人惊异的;令人大为惊奇的”;amazed “吃惊的,惊奇的”.which引导的是非限制性定语从句,修饰carelessness,所以谓语动词用单数形式was. 6．These three college students are real heroes because they risked________their own lives in order to save the drowning boys in the water. A．having lost
B．to lose C．losing
D．of losing 解析：选C.句意：这三个大学生是真正的英雄,因为他们冒着失去生命的危险去救那些溺水的男孩.考查risk构成的短语risk doing sth.冒险做某事. 7．—Why didn’t you go fishing with your friend yesterday? —Well,fishing is a hobby which calls for a great deal of ________,which I don’t have. A．money
B．wisdom C．patience
D．strength 解析：选C.考查名词词义辨析.答句句意：“钓鱼是一项需要很大耐心的爱好,而我没有耐心.”money“钱”;wisdom“智慧,聪明”;patience “耐心,毅力”;strength“力气,力量”。 8．People have always been________about exactly how life on earth began. A．curious
B．excited C．anxious
D．careful 解析：选A.考查形容词词义辨析.句意：人们一直对地球上的生命到底是如何产生的很好奇.be curious about “对……好奇;想知道”,符合题意.excited “兴奋 的,激动的”;anxious“忧虑的,担心的”; careful “小心的,细心的”. 考点串讲?讲练互动 单词精研 1differ vi.不同于,区别于 (教材P23)How do the tourists differ from local people？ 游客与本地人有什么不同？(怎样区分游客与本地人？) 归纳拓展 ①We differ with them on/about the question. 我们在那个问题上跟他们的意见不同. ②We and the foreigners differ in many ways. 我们和这些外国人在许多方面不同. ③English differs_from Chinese in this respect. 在这方面英语不同于汉语. ④Everyone fails now and then.It is how you react that makes_a_difference in life. 每个人都会失败,重要的是你如何对待. 2anxious adj.忧虑的,担心的 (教材P23)From that moment they started to feel anxious and they slept badly that night. 从那时起他们开始感到忧虑并且那晚他们失眠了. 归纳拓展 ①I am anxious about his safety.我担心他的安全. ②He is_anxious_for promotion.他很想得到提升. ③I was_anxious_for everything to be settled. 我渴望每一件事都被安排妥当. ④(2011·高考广东卷)Studies have shown that to be bored is to be anxious.研究表明心烦就是忧虑.
辨析
anxious,eager,keen anxious 强调因忧虑、关注或害怕而产生的急切心情. eager 侧重于急于成功的迫切心情. keen 强调因兴趣强烈或欲望而急于做某事. 3risk vt.冒……的危险 n．[C,U]危 险,风险 (教材P116)What makes people risk their lives to do them？ 是什么促使人们冒着生命危险去做它们呢？
归纳拓展 ①He risked his life to save her. 他冒着生命危险去救她. ②They knew they risked_being arrested. 他们知道自己冒着被捕的危险. ③We don’t want to run the risk of losing their business. 我们不想冒险失去他们的生意. ④(2011·高考浙江卷)Now,even at_the_risk_of having Brother caught to beat carpets,they had sent him to the kitchen for more string (线).现在,尽管有使弟弟被撞见殴打木匠的可能,但是他们还是派他去厨房拉墨线.
4amaze vt.使大为吃惊,使感到惊愕
(教材P26)Marco,in turn,was amazed by how beautiful and powerful China was. 马可也相应地被中国的美丽和强大所震撼.
归纳拓展 ①Visitors were amazed at the achievements in the car manufacture of the city during the past decade.参观者对这城市过去十年中汽车制造工业的成就感到惊奇. ②We were_amazed_to find that no one was hurt. 我们很惊异地发现竟没有人受伤.
③(2010·高考天津卷)“I’m just amazed you still have the same stand for holding the pad and pencil after all these years.”“我只是很惊讶你在这么多年之后还仍然保留着放铅笔和便条纸薄的木架.”
5confuse vt.混淆,弄乱;使困惑 (教材P26)He was also confused by the black stones people used to burn for fuel. 人们用来当燃料的黑色石头使他感到困惑.
归纳拓展 ①Don’t give me so much information－you’re confusing me.别跟我说那么多消息,你都要把我搞糊涂了. ②(2010·高考上海卷)Finally,have I included too many unnecessary details that may confuse readers？最终,是不是我包含了太多的使读者迷惑的不必要的细节？ 辨析
confuse,puzzle confuse 常用来指令人头脑混乱或异常惊讶,有时强调惊慌失措. puzzle 常用来指对不能理解的事物感到迷惑. 6quantity n．量,数量 (教材P27)He went to a city where iron was produced in huge quantities. 他去了一个城市,在那里铁被大量生产出来.
归纳拓展 ①We export a large quantity of bicycles now. 我们现在出口大量的自行车. ②There is a small quantity of water left in the bottle. 瓶子里还剩下少量的水. ③Large_quantities_of water have been polluted by the factory.大量的水已经被那座工厂污染了. ④I can ask him if he can give us a better price if we buy in_quantity/in_large_quantities.如果我们要大量购买的话,我可以问他能不能给我们一个更优惠的价格.
【重点提示】 a quantity of和quantities of其后既可以接可数名词复数,也可以接不可数名词.一般来说,“a quantity of＋名词”作主语时,谓语动词与名词保持数的一致;而“quantities of＋名词”作主语时,谓语动词与quantities保持数的一致. 7preparation n．准备;预备 (教材P28)．..both teams organised food bases in preparation for their journeys the next year. ……两个队都筹建食物储存处,为下一年的旅行做准备.
归纳拓展 辨析
prepare,prepare for prepare “准备”,谓语动词直接体现在宾语上. prepare for
“为……做准备”,for的宾语一般只是谓语动作所要达到的目的. 助 记
Unit 8 Adventure——探险 必修三 1．...until...“直到……时候”;not...until...“直到……才……” The meeting was put off until ten o’clock.会议推迟到十点钟. 句型公式?妙笔生花 Not until all the fish died in the river did the villagers realize how serious the pollution was.(倒装句) 等到湖里的鱼全死光了,村民们才意识到污染是多么严重.
2．unless...“除非,如果不……”(＝if...not) I won’t attend his birthday party unless invited(＝unless I am invited)．除非被邀请,否则我不会去参加他的生日晚会. 3．主语＋be doing...when...“正在做某事,这时……” I was walking along the river when I heard a drowning boy cry for help. 我正在河边散步,这时我突然听到一个落水男孩求救. 4．主语＋be about to do...when.../主语＋be on the point of(doing)．..when...“刚要……这时……” I was about to leave when it began to rain.我刚要离开,这时下雨了. 5．主语＋had done...when...“刚做完……这时……” I had just finished my exam paper when the bell rang,announcing the class was over.我刚做完作业,这时下课铃响了.
基础盘点?自测自评 核心单词 1．__________adj.最大的,最多的 2．__________adj.忧虑的,担心的→__________adv.焦虑地→anxiety n．忧虑,焦虑 maximum anxious anxiously 3．__________n．量,数量→quality n．质量 4．__________vt.震惊,惊骇 5．__________n．志向,抱负→__________adj.有志向的 6．__________adj.没有希望的→__________v．&n.希望 quantity shock ambition ambitious hopeless hope 7．__________vt.运转,起作用 8．__________n．国籍→________n．国家→__________adj.国家的 9．__________vt.&n.运输,运送→_______________n．运输 10．____________adj.主要的,较重要的→__________n．大多数
function nationality nation national transport transportation major majority 11．__________vi.不同于,有区别→difference n．不同,差异 12．__________adj.极度的,极端的→__________adv.极度地 13．__________n．相似性,类似性→__________adj.相似的,类似的 differ extreme extremely similarity similar 14．__________vt.冒……的危险→__________adj.冒险的 15．She reaches the limit of her__________(耐心)easily because she is very__________(没有耐心的) with students who cannot follow her. risk risky patience impatient 16．The__________(幸存者)in the earthquake were rushed to the nearest hospitals.The army were still searching to see if someone else_________(幸存)．
survivors survived 高频短语 1．________________ 起飞 2．________________
就在此刻 3．________________ 为了(某一目的) 4．________________ 颠倒地,倒置地 5．________________ 出现,到场 take off right now in order to upside down turn up 6．________________决定不履行(允诺的事) 7．________________使理解(某事) 8．________________轮流 9．________________(坏事)突然发生,爆发 10．________________关进监狱 back out get across in turn break out put into prison 11．________________坚持(某种)说法;袖手旁观 12．________________在途中 13．________________损坏,不能运转 14．________________用完,耗尽 15．________________继续做某事 stand by on one’s way break down run out of carry on 典型句式 1．特殊疑问词(what/why/how/when...)＋一般疑问句(do you think/suppose/imagine...)构成的混合疑问句 ______________________(你认为为什么)people would want to go on this trip? Why do you think 2．It is ＋adj.＋to do sth.结构 __________________________________(很难理解)how exciting it is! It’s difficult to get across 3．have experience in doing sth.有做某事的经验 All our guides __________________________________ (在……方面有数年的经验) leading hiking trips in the Himalayas. have several years of experience in 4．too...to...结构表示“太……而不能……” Although people enjoyed reading his book,many of them thought that Marco’s stories about China were_____________________ (太离奇而不可信)． too fantastic to be true 5．表地点或时间的副词置于句首构成的完全倒装句 ____________ (接着到来) the total darkness of the polar winter. Then came 单元语法 定语从句(Ⅲ) 1．(2016·沈阳四校协作体阶段测试)In Western culture,21 was the age________young people traditionally received a key to their parents’ door,as a symbol of entering adulthood.
A．in which B．on which C．at which
D．to which 解析：选C.本句中的先行词是the age,先行词在从句中作时间状语,即at the age of 21.所以这里选C.
2．(2016·温州五校联考)It was in the garden of his old house________he grew up that he dug up a pot of gold. A．that
B．where C．which
D．what 解析：选B.where引导定语从句,修饰先行词house,并在定语从句中作状语.另外,这是一个强调句,被强调部分是in the garden of his old house________he grew up. 3．(2016·温州五校联考)He came back late,________which time all the guests had already left. A．after
B．by C．at
D．during 解析：选B.考查定语从句中介词的选择.by在这里表示“到……为止,不迟于……”,即到他回来时,所有客人都已经离开了. 4．(2016·西安五校模拟)Faye’s fondest memory is of last year,________the club gave a tea party for her birthday. A．that
B．which C．where
D．when 解析：选D.定语从句题的解题关键是在主句中找出先行词,然后把先行词“代入”从句中,判断其在从句中的“地位”和“作用”,此处先行词为last year,在定语从句中作时间状语,应该用关系副词when,故选D. 5．(2016·温州五校联考)The British are not so familiar with different cultures and other ways of doing things,________is often the case in other countries. A．what
B．As C．so
D．that 解析：选B.as在这里引导非限制性定语从句,as代指前面整个句子的内容,而且as在从句中作主语.