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| 动词不定式作主语时,常用it作形式主语,而将真正的主语放在句末,避免句子头重脚轻。其结构为It+be+adj.+to do sth. | To learn English well is useful.=It is useful to learn English well. |
如果要说明不定式表示的动作的执行者,可以在不定式前加一个for短语。其结构为It+be+adj.+for sb.+to do sth. | It is good for you to go out for a walk. |
某些表示人的品质、特征等的形容词(如kind,good,nice,wise,clever,polite等)作表语时,不定式之前可以加一个of短语,用来说明动作的执行者。其结构为It+be+adj.+of sb.+to do sth. | It’s not polite of him to speak to old people like that. |
两个或两个以上的动词不定式并列时,第一个不定式带to,后面的不定式通常省略to | To go to sleep early and get up early is a good habit. |
| 不定式用在及物动词后作宾语,常见的及物动词有:begin,choose,continue,decide,expect,fail,forget,hate,help,hope,learn,manage,mean,need,offer,plan,prefer,pretend,promise,refuse,try,afford,agree,start,like等 | I can’t afford to buy a digital camera at the moment. |
在find,think后跟不定式作宾语时,常用it代替,而将真正的宾语放在后面 | I find it easy to read English every day. |
| 常接不定式作宾语补足语的动词有:want,ask,tell,allow,get,would like,advise,encourage等 | My mother encourages me to learn Japanese. |
一些使役动词和感官动词也用不定式作宾补,这时不定式要省略to。这些动词有:一感(feel)、二听(hear,listen to)、三让(let,make,have)、四看(look at,see,watch,notice)。但变被动语态时必须加上to | I often hear Li Ming sing in the next room. |
动词help后面的不定式,既可以带to,也可以不带to | You must help me(to)do my homework this afternoon. |
| | I have some clothes to wash. |
如果不定式是不及物动词,且与它所修饰的词构成逻辑上的被动关系,则不定式要加上相应的介词 | He is looking for a room to live in.We have a lot of things to talk about. |
当不定式修饰的名词是time,place或way时,不定式后面习惯上省略介词 | My grandma had no place to live(in)in the old days. |
不定式修饰 something,anything,nothing时,放在它们的后面,如果something,anything,nothing有形容词修饰,词序是“something/anything/nothing+形容词+不定式” | I had something cold to drink. |
| | To be a good student,one must study hard. |
和某些形容词连用构成“be+形容词+不定式”结构,作原因状语 | We are sorry to trouble you. |
作程度或结果状语时,常与enough(表示肯定)或too(表示否定)连用 | He is old enough to go to school.He is too young to go to school. |
| 表示主语的“职业、职责或性质”等,通常对连系动词前面的名词进行解释说明 | His wish is to become a doctor. |
| 不定式常和疑问词what,which,when,where,how连用,在句中担当主语、宾语、表语等成分 | He didn't know where to go.=He didn't know where he should go. |