You can’t be when you camp a high altitude, the air is thin.
A. enough careful; at; which
B. too careful; at; where
C. careful enough; on;at which
D. too careful; on; that
网友回答
A. enough careful; at; which
(答案→)B. too careful; at; where
C. careful enough; on;at which
D. too careful; on; that
解析：第一空考查短语：can’t… too 再什么也不为过，第二空考查短语：at a high altitude以很高的海拔，第三空考查定语从句，先行词为a high altitude，从句中缺少地点状语。所以选B。