Unit 13 We’re trying to save the earth单元语法小专题(Grammar Focus)语法精讲一、情态动词用法回顾情态动词有can(could)，may(might)，must，have to，shall(should)，will(would)，dare(dared)，need等情态动词无人称和数的变化；不能单独使用，必须与其后的动词原形构成谓语1．情态动词的一般用法(1)can，could①表示能力(体力、知识、技能)can表示现在的能力，could表示过去的能力②表示请求和允许此时可与may互换在疑问句中还可用could，might代替，不是过去式，只是语气更委婉，不能用于肯定句和答语中如：—Could I come to see you tomorrow？我明天可以来看你吗？—Yes，you can./No，I'm afraid not.是的，可以/不，恐怕不行③表示客观可能性(客观原因形成的能力)辨析】can与be able tocan表示能力时，可与be able to换用；can只有一般现在时和一般过去时两种时态，而be able to可用于多种时态。
如：What else can you see in the sky? ＝What else are you able to see in the sky? 在天空中你还能看见别的什么？They will be able to come back in about twenty minutes.他们大约能在20分钟后回来2)may，might①表示请求和允许might比 may语气更委婉，而不是过去式否定回答时可用can't或mustn't，表示“不可以，禁止”用“May I…？”征询对方许可时比较正式和客气，而用“Can I…？”在口语中更常见②用于祈使句，表示祝愿如：May you succeed！愿你成功！(3)must，have to①表示必须、必要在回答由must引出的问句时，如果是否定的，不能用mustn't(禁止，不准)，而用needn't或don't have to(不必)如：—Must we hand in our exercise books today? 我们今天必须交练习本吗？—Yes，you must.(No，you don't have to/you needn't.)是的，你们必须今天交。
不，你们不一定要今天交)②must是说话人的主观看法，而have to则强调客观需要must只有一般现在时，而have to 有更多的时态形式如：I had to work when I was your age.我像你这么大时，就必须工作了4)dare，need①dare作情态动词用时，常用于疑问句、否定句和条件从句中，其过去式为dared如：He daren't speak English before such a crowd，dare he? 他不敢在人群前说英语，是吗？②need 作情态动词用时，常用于疑问句、否定句在肯定句中一般用must，have to，should代替如：—Need I finish the work today？我需要今天完成这个工作吗？—Yes，you must./No，you needn't.是的，必须今天完成/不，不一定要今天完成注意】dare和 need也可作实义动词用，此时有人称、时态和数的变化在肯定句中，dare后面常接带to的不定式在疑问句和否定句中，dare后面可接带to或不带to的不定式而need后面只能接带to的不定式如：He doesn't dare(to) answer.他不敢回答。
He needs to finish his homework today.他今天要完成家庭作业5)shall，should①shall 用于第一人称，征求对方的意见shall 用于第二、三人称，表示说话人给对方的命令、警告、允诺或威胁如：What shall we do this evening? 今天晚上我们做什么？You shall fail if you don't work hard.如果你不努力就会失败警告)②should意为“应该”，通常表示劝告、建议等如：I should help her because she is in trouble.我应该帮她，因为她陷入麻烦了You should go to class right away.你应该马上去上课Should I open the window? 我应该打开门吗？(6)will，would①表示请求、建议等，would更委婉如：Will/Would you pass me the ball，please? 你能把那个球递给我吗？②表示意志、愿望和决心如：I will never do that again.我再不会那样做了。
③would表示过去反复发生的动作或某种倾向如：During the vacation，he would visit me every other day.假期里，他每隔一天看我一次2．情态动词表推测(1)can表示推测(惊讶、怀疑、不相信的态度)，通常用于疑问句、否定句中如：Can this be true？这可能是真的吗？This can't be done by him.这不可能是他做的2)may/might表示推测、可能性(不用于疑问句)might不是过去式，它所表示的可能性比may小如：Your mother may/might not know the truth.你妈妈可能不知道真相3)must表示可能性极大的主观推测，只用于肯定的陈述句中如：You're Tom's good friend，so you must know what he likes best.你是汤姆的好朋友，你一定知道他最喜欢什么He must be home by now.他现在一定回家了二、used to用法回顾1．used to后接动词原形，表示过去经常性或持续性的动作或状态，意为“过去常常”。
如：My mother used to go shopping on weekends.我母亲过去常在周末购物When I was young，it used to be very cold in winter.我小的时候，冬天经常很冷2．used to的否定形式为“didn't use to do sth.”或“usedn't to do sth.”；一般疑问形式为“Used＋主语＋to do sth.”或“Did＋主语＋use to do sth.”；附加疑问句式为“usedn't＋主语”或“didn't＋主语”如：I didn't use to like singing./I used not to like singing.我过去不喜欢唱歌Did you use to play football？/Used you to play football? 你过去常常踢足球吗？【拓展】(1)be/get used to(doing) sth.表示“习惯于(做)某事”，其中to为介词如：He is used to living in the city.他习惯于住在城市2)be used to do/for doing sth.表示“被用于做某事”，其中的be used是被动语态结构。
如：Wood can be used to make/for making furniture.木材可用于制造家具语法精练Ⅰ.用can，may，must，need或have to的适当形式填空1．You must return the book to the library on time.2．I can't(not)find the way to the hospital.Could you show me the way?3．—Must I finish the work right now?—No，you needn't(not)．You may do it later.4．He said he couldn't(not) come tonight.5．Her mother was ill.She had__to stay at home and look after her.6．It's time for class.You must stop playing football or you may be late for class.7．The cloud is lifting，so it can't(not) be a rainy day tomorrow.8．The desk is not dirty. You needn't clean it.9．—What is your mother going to do this Saturday?—I'm not sure. She may/might go to see my grandmother.10．If the traffic light is red，you mustn't cross the road.It's dangerous.Ⅱ.用括号内所给单词的适当形式填空。
11．We don't need to__work(work) today.12．He doesn't dare to__break(break) his promise.13．Some students are used to asking(ask) their parents for help when they meet trouble.14．There used to__be(be) a quiet village here.15．I think you will be used to living(live) in the countryside.16．All of us know that cotton can be used to__make(make) cloth.17．You used to__go(go) to school by bike，didn't you?Ⅲ.根据汉语意思完成句子，每空一词18．这本书一定是汤姆的，他的名字在封面上This book must be Tom's. His name is on the cover.19．他被一个5岁的小男孩愚弄了，这可能是真的吗？Can it be true that he was fooled by a five－year－old boy?20．你的车需要维修了。
Your car needs repairing. 21．这种小刀是用来切东西的This kind of knife is used to cut things.22．当我年轻的时候，我常常打篮球I used to play basketball when I was young.23．他过去常花很多时间玩电脑游戏吗？Did he use to spend much time playing computer games?。