In western culture,21 was the age young people traditionally received a key to their parents’ door, as a symbol of entering adulthood.
A. in which
B. on which
C. at which
D. to which
网友回答
A. in which
B. on which
(答案→)C. at which
D. to which
解析：本题考查定语从句。先行词age与介词at搭配。句意：在西方传统文化中，年轻人到了21岁便可获得进入父母房间的钥匙，象征着他们开始进入成人世界。