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動詞不定式作主語時,常用it作形式主語,而將真正的主語放在句末,避免句子頭重腳輕。其結(jié)構(gòu)為It+be+adj.+to do sth.
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To learn English well is useful.
=It is useful to learn English well.
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如果要說明不定式表示的動作的執(zhí)行者,可以在不定式前加一個for短語。其結(jié)構(gòu)為It+be+adj.+for sb.+to do sth.
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It is good for you to go out for a walk.
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某些表示人的品質(zhì)、特征等的形容詞(如kind,good,nice,wise,clever,polite等)作表語時,不定式之前可以加一個of短語,用來說明動作的執(zhí)行者。其結(jié)構(gòu)為It+be+adj.+of sb.+to do sth.
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It’s not polite of him to speak to old people like that.
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兩個或兩個以上的動詞不定式并列時,第一個不定式帶to,后面的不定式通常省略to
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To go to sleep early and get up early is a good habit.
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不定式用在及物動詞后作賓語,常見的及物動詞有: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
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I can’t afford to buy a digital camera at the moment.
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在find,think后跟不定式作賓語時,常用it代替,而將真正的賓語放在后面
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I find it easy to read English every day.
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常接不定式作賓語補(bǔ)足語的動詞有:want,ask,tell,allow,get,would like,advise,encourage等
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My mother encourages me to learn Japanese.
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一些使役動詞和感官動詞也用不定式作賓補(bǔ),這時不定式要省略to。這些動詞有:一感(feel)、二聽(hear,listen to)、三讓(let,make,have)、四看(look at,see,watch,notice)。但變被動語態(tài)時必須加上to
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I often hear Li Ming sing in the next room.
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動詞help后面的不定式,既可以帶to,也可以不帶to
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You must help me(to)do my homework this afternoon.
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I have some clothes to wash.
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如果不定式是不及物動詞,且與它所修飾的詞構(gòu)成邏輯上的被動關(guān)系,則不定式要加上相應(yīng)的介詞
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He is looking for a room to live in.
We have a lot of things to talk about.
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當(dāng)不定式修飾的名詞是time,place或way時,不定式后面習(xí)慣上省略介詞
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My grandma had no place to live(in)in the old days.
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不定式修飾 something,anything,nothing時,放在它們的后面,如果something,anything,nothing有形容詞修飾,詞序是“something/anything/nothing+形容詞+不定式”
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I had something cold to drink.
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To be a good student,one must study hard.
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和某些形容詞連用構(gòu)成“be+形容詞+不定式”結(jié)構(gòu),作原因狀語
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We are sorry to trouble you.
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作程度或結(jié)果狀語時,常與enough(表示肯定)或too(表示否定)連用
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He is old enough to go to school.
He is too young to go to school.
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表示主語的“職業(yè)、職責(zé)或性質(zhì)”等,通常對連系動詞前面的名詞進(jìn)行解釋說明
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His wish is to become a doctor.
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不定式常和疑問詞what,which,when,where,how連用,在句中擔(dān)當(dāng)主語、賓語、表語等成分
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He didn't know where to go.
=He didn't know where he should go.
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