问题补充：
Mr Green didn’t know last night.
A. when does his son come back
B. when his son comes back
C. when his son come home
D. when his son came home
答案：
A. when does his son come back
B. when his son comes back
C. when his son come home
(答案→)D. when his son came home
解析：动词know后跟的是一个宾语从句，要用陈述句的顺序，故A不正确，主句是过去
时，从句要用过去时一种，只有D用的是过去时，故选D。
