Cold the night air was, he slept soundly because he was so tired after working for a whol

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A. although
B. while
C. however
(答案→)D. as
解析：本题重在掌握as“尽管”时可引起倒装，同时although引导让步状语从句时不能倒装，as引导让步状语从句时必须倒装，而though引导让步状语从句时可以倒装也可以不倒装。本句中的Cold as the night air was=Though the night air was cold。句义：尽管晚上的空气很冷，但是因为工作了一整天以后他很累，所以他还是睡得很好。故D正确。