Some aspects of a pilot’s job be boring,and pilots often work at inconvenient hours.
A. can; have to
B. may; have to
C. have to; may
D. ought to; must
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(答案→)A. can; have to
B. may; have to
C. have to; may
D. ought to; must
解析：句意为“做一个宇航员某些方面可能很乏味，而且他们常常不得不在很不适宜的时候工作”。第一空表示在某种情况下“可能会”，用can; 第二空表示客观情况下“必须”，用have to。