问题
选择题
(2013·湖南高考)He ________ sleep, although he tried to, when he got on such a hunt for an idea until he had caught it.
A．wouldn't
B．shouldn't
C．couldn't
D．mustn't
答案
答案：C
选C 考查情态动词。句意：尽管他想睡，但仍睡不着，(因为)当时他拼命想着一个主意，一直到想出来为止他才睡去。此处couldn't表示“不可能”，符合句意。