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這個could 后該接不定式還是動詞原形

有這樣一道選擇題：

The soldiers tried their best and did what they could _________ against the flood.

A. fight                        B. to fight                        C. fighting                        D. fought

有的同學一看到空格前的情態動詞 could 就斷定此處應填動詞原形 fight，即斷定選A答案。其實選錯了，正確答案應是B。這是一個省略句，即在 could 后省略了動詞 do，若把句子補完整應為The soldiers tried their best and did what they could do to fight against the flood (士兵們竭盡全力抗洪)。即句中的不定式短語 (to fight against the flood) 用作目的狀語的，而不是與情態動詞(could)一起構成謂語。請再看類似例句：

(1) He did what he could to help us. 他盡力幫助我們。

(2) He saved what he could to buy a car. 他盡量節約每一分錢以便買車。

(3) He ran as fast as he could to catch the early bus. 他拼命地跑以便趕上早班車。

至此，有的同學可能又會想當然地認為，今后只要遇到類似結構的題選帶to不定式就萬事大吉了，但也不一定，例外還是有的，還得具體問題具體分析。請看下例：

(4) He ran as fast as he could _________ to catch the early bus.

A. to hope                        B. hope                        C. hoping                        D. hoped

若根據以上“經驗”認為此題要選A答案，那就又錯了。此題應選 C，其中的現在分詞短語 hoping to catch the early bus 用作伴隨狀語。

(5) He spent every minute he could _________ spoken English.

A. practise                        B. to practise              C. practising                      D. practised

【分析】此題應選 C，它與以上各題的情形均有所不同，雖然與上面的第(4)題的答案一樣，均為動詞的 –ing 形式，但也不完全一樣：第(4)的 hoping 為現在分詞，在句中用作伴隨狀語；而此題的 practising 是動名詞，之所以用它與前面動詞 spent 的搭配有關，即 spend … (in) doing sth。若將此句補充完整，即為 He spent every minute he could spend in practising spoken English.

(6) Mr Smith made up his mind to devote all he could _________ his oral English before going abroad.

A. improve                      B. to improve                 C. improving                     D. to improving

【分析】此題答案選D，注意兩點：一是 devote … to … 是固定搭配，意為“把……貢獻給……”；二是其中的 to 是介詞，不是不定式符號，后接動詞時要用動名詞。