问题补充：
He has been working hard day and night, which, of course,his tiredness.
A. answers for
B. accounts for
C. applies for
D. stands for
答案：
A. answers for
(答案→)B. accounts for
C. applies for
D. stands for
解析：考查短语辨析。answers for回答，accounts for做出解释，applies for申请，stands for代表，句意：他一直日日夜夜的工作，当热这就能解释他劳累的原因了。故选B。
