The old man often looked back on the past days he worked hard to make a living.A. whichB

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A. which
(答案→)B. when
C. where
D. that
解析：B　考查定语从句。句意：这个老人经常回顾他过去辛苦谋生的日子。分析句子成分可知，先行词为the past days，空处在定语从句中充当时间状语，故用when引导。