(2012·全国卷Ⅰ)I use a clock to wake me up because at six o'clock each morning the train es by my house.
A. couldn't
B. mustn't
C. shouldn't
D. needn't
网友回答
A. couldn't
B. mustn't
C. shouldn't
(答案→)D. needn't
解析：选D 考查情态动词。句意：我不需要用闹钟叫自己起床，因为每天早上六点都会有一列火车经过我家门口。应选“不需要”，即needn't。