有這樣一道題：Everyone in our class was working hard and doing what we could _________ a good college.
A. enter B. to enter C. entering D. entered
【分析】容易誤選A。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 enter。其實，此題正確答案應是B。此句爲省略句，即在 could 後省略了動詞 do，若把句子補完整應爲Everyone in our class was working hard and doing what we could do to enter a good college。即句中的不定式短語(to enter a good college)是用作目的狀語的，而不是與情態動詞(could)一起構成謂語。請再看類似例句：(could)
(1) They did what they could to comfort her. 他們儘量安慰她。
(2) They did everything they could to save her life. 他們盡一切力量拯救她的性命。
(3) He studies as hard as he could to catch up with his classmates. 他拼命學習以便趕上他的同學。值得指出的是，這也並不是說今後只要遇到類似結構的題就一定選帶to不定式。請看以下試題：
(4) He ran as fast as he could _________ to catch the early bus.
A. to hope B. hope C. hoping D. hoped此題的答案是 C不是A，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
此題答案選 C，這SPAN lang=E與前面動詞 spent 的搭配有關，即 spend … (in) doing sth。若將此句補充完整，即爲 He spent every minute he could spend in practising spoken English.
(6) Before going abroad he devoted all he could __________ his oral English.
A. improve B. to improve C. improving D. to improving
此題答案選D，注意兩點：一是 devote … to … 是固定搭配，意爲“把……貢獻給……”；二是其中的 to 是介詞，不是不定式符號，後接動詞時要用動名詞。
