九年级英语Unit13 《 We27re trying to save the earth!》知识点4 如果句子里面没有时间状语,汉语意思能够加“已经”,往往用现在完成时态。
Have you lost your library book?你已经弄丢了从图书馆借的那本书吗？5现在完成时态还常常用于下列句型They have planted many trees in the last/past few years.This is the best book I have ever read.在现在完成时中,一次性动词不能和一段时间状语连用例： He has bought the book for 3 years.（错）因 buy 这个一次性动词不能和一段时间for 3 years连用,改正的办法有：He has bought the book.(去掉一段时间for 3 years)He bought the book 3 years ago(改为一般过去时, 使句子的意思不变) It ’ s/It has been 3 years since he bo ught the book. = 3 years has passed since he bought the book.（改为固定句型It is/It has been --- since--- ）He has had the book for 3 years.（用延续性动词have 代替 buy ）另外①（错）改为： I have been here for 3 years.②leave/go →be awa yHe has left for 3 hours.（错）改为： He has been away for 3 hours.③ begin/start→be onThe film has begun for 3 minutes.（错）改为： The film has been on for 3 minutes.④ open →be open / close→ be closedThe shop has opened for 3 years.(错)改为： The shop has been open for 3 years.⑤ die→be deadHis father has died for 3 years.(错)改为： His father has been dead for 3 years.⑥ finish/end→ be overHe has finished the work for 3 days.(错)改为： The work has been over for 3 days⑦ join I have joined the army for 3 years.（错）改为： I have been in the army for 3 years.或I have been a soldier for 3 years.⑧ buy /catch→ haveI have bought the bike for 3 years.（错）改为： I have had the bike for 3 years.He has caught a cold for 3 days.（错）改为： He has had a cold for 3 days.⑨borrow → keepI have borrowed the book for 3 years.（错）改为： I have kept the book for 3 years.还有其它的归纳如下：5.情态动词1)情态动词本身有一定的词义 ,表示说话人的情绪、态度或语气 ,但不能单独作谓语 ,只能与其他动词构成谓语。
常见的有：can (could), may (might), must, need,等。
2)情态动词无人称和数的变化 , 后接动词原形。
否定式是在情态动词后面加not 。
个别情态动词有过去式形式, 也可用来表达更加客气、委婉的语气。
shall (should), will (would)1.can 和 could 的用法(1)can/could 表示“能力；可；可能性”等。
could can 的去式。
如： CanI use your bike?(2)can 用在疑句中 ,表示征求意、求可,答仍用can; could 用在疑句中 ,比 can 更委婉、客气 ,是一种礼貌的法, 并不表示去 ,答用 can, 而不能用 could 。
如：—Could you tell me the way to the zoo? — Sorry. I can't. I'm new here 。
[注意 ] can 和 could 只能用于在和去两种,将来中用 be able to。
另外 , can't 可表示否定推。
如： That ______ be Mr Wang. He has goneto Beijing 。
2.may 和 might 的用法may/might 意“可以”,表示同意、可或求方可,也可表示祝愿。
may 的否定形式may not 。
might 是 may 的去式 ,有两种用法：一种表示去式；一种表示虚气,使气更加委婉、客气,或表示可能性更小。
以may 开的一般疑句 ,其否定回答用mustn't,而不用may not 。
如： ______ I use your pen? 我可以用你用的笔？You may put on more clothes. May you be happy!Might I borrow some money now?He might be alive.3.must 的用法must意“必,一定,准是”,表示人有必要做某事, 或命令、要求人做某事以及事物的推。
否定形式mustn't,表示“不得”一,“定不要”。
如：I ______ finish my work today。
You mustn't drive after drinking。
(1)must 与 have to 的区： must 表示人的主意愿； have to 表示客需要。
如：I must do my homework first。
It is raining hard outside; I _____ stay athome 。
(2)回答由 must 引的疑句的提①肯定回答： Yes, ⋯must. 如：— Must I go home now? — Yes, you must. ②否定回答：No,⋯needn't./No,⋯don't/doesn't have to.— Must I go home now? — No, you __ ____.(3)must 表示事物的推 ,意“想必；一定”,只用于肯定句中；表“推” ,情与原形 ,(常 be )用 ,如： The man must be our teacher 。
4.need 的用法(1)need表示“需要,必”,主要用于否定句和疑句中。
其否定形式needn't, 表示“没有必要 ,不必”；由 need 构成的疑句行回答 ,其肯定回答用 must, 否定回答用needn't 。
如— Need we do some cleaning now?— Yes, you must. — No, you needn't.(2)need可作,常用于下列构：①人： need to do sth“需要做某事”。
如I need to learn more.②物： need doing“某物需要被做”=need to be done。
如： My hair needs cutting. =My hair needs to be cut.③ need + 名或代。
如：All living things need water.5.shall 和 should 的用法shall 用于第一人称的句子中,表示提建或求；should 用于各种人称的句子中,或任 ,意“ ”。
如： ______ we go out for a walk?You should study hard at school。
should have done主要有两个用法：用于推去已生的情况。
如：He should have arrived by now.用于指本生而上未生的情况。
如：You should have told me so before.6.will 和 would 的用法will 用于第二人称疑句,表示征求意或提建；would will 的去式 ,可用于多种人称,表示意愿。
如：Will you have a little soup?would have done主要有两个用法：表“猜去”I guess the poet would have been about twenty when she wrote her first poem.表“ 去本会生 ,而并未生”,没有之意。
I would have written before but I have been ill.本来我是会写信的,但是由于我生病了。
（用来明某一情况,没有之意）7.have tohave to的述句形式肯定式： have to +原形I have to tidy my room.我得整理房.否定式： don't (doesn't) + have to +原形You don't have to go if you don't want to.have to的一般疑句形式及略答have to 的一般疑形式必借助助do 或 does ：Do you have to look after your sister? Yes,I do./ No,I don't.have to的特殊疑句形式What do you have to do on Sundays?have to可用于各种A、一般在：I have to visit Mr Wang.B、一般去：That night we had to walk home because there was no bus.C、一般将来：We'll have to ask Zhang Ming instead.D、与 may 用： I think he may have to help his Dad in the garden.8.ought toought to 的肯定式当,You don't look well. You ought to go to see the doctor.ought to 的否定式和疑式ought to 的否定形式是 ought 后直接加 not 构成 ,其否定形式可写 oughtn't 。