The reason he explained for his being late was his alarm clock didn’t work.
A. why; because
B. that; because
C. /; that
D. for which; that
网友回答
A. why; because
B. that; because
(答案→)C. /; that
D. for which; that
解析：第一空为定语从句先行词是The reason关系词要在从句中做explained的宾语所以要用关系代词which\that还可省略；第二空考查表语从句不缺成分用连接词that，所以答案为C