Some aspects of a pilot's job be boring, and pilots often work at inconvenient hours．
A. can ; have to
B. may ; can
C. have to; may
D. ought to; must
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(答案→)A. can ; have to
B. may ; can
C. have to; may
D. ought to; must
解析：考查情态动词:第一空填can，表示“有客观的可能性”，第二空填have to表示不得不，句意：某些方面，飞行员的工作可能很乏味，飞行员经常在不方便的时候工作。选A。