问题补充：
-Do you know?
-Two weeks ago.
A. when did John join the club
B. how often does Jolm drink milk
C. when John arrived in China
D. how soon will John come back
答案：
A. when did John join the club
B. how often does Jolm drink milk
(答案→)C. when John arrived in China
D. how soon will John come back
解析：句意：---你知道John什么时候参加俱乐部？---两个星期前。宾语从句采用陈述语气。答句是回答时间，因此应用when问。根据题意，故选C。
