His father often es back from work at 10 o’clock at night his mother is waiting for him.
A. that
B. when
C. where
D. which
网友回答
A. that
(答案→)B. when
C. where
D. which
解析：考查定语从句。定语从句的先行词是指代时间的10 o’clock，定语从句的结构很完整，故使用关系副词when。句意：他的父亲常常在晚上10点回家，在那时他的妈妈正在等着他。故B正确。