Mountain climbing be really dangerous at times even though it is challenging and exciting in general.
A. can
B. should
C. shall
D. must
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(答案→)A. can
B. should
C. shall
D. must
解析：句意：爬山有时可能真的很危险，纵然总得来说，它很令人激动，又具有挑战性。Can可能；should 应该；shall将要；must必须，选A。