need 表示“需要”或“必須”,作情態(tài)動(dòng)詞時(shí),僅用于否定句或疑問(wèn)句中.
在肯定句中一般用must,have to,ought to或should 代替.例如：
You needn't come so early.
Need I finish the work today?－－Yes,you must.
注意：needn't have done“表示本來(lái)不必做某事而實(shí)際上做了某事”.例如：You needn't have waited for me.
“should have done”表示應(yīng)該做到而實(shí)際上沒(méi)有做到.
You should have started earlier.
“ought to have done”表示過(guò)去應(yīng)做某事而實(shí)際未做.
You ought to have helped him (but you didn't)
切記：need作情態(tài)動(dòng)詞時(shí)僅用于否定句或疑問(wèn)句中在肯定句中一般用must,have to,ought to或should代替
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