问题补充：
——Where did you come across our chemistry teacher ?
------ It was in the supermarket I purchased mooncakes.
A. that
B. which
C. where
D. when
答案：
A. that
B. which
(答案→)C. where
D. when
解析：本题考查强调句的省略用法，被强调部分是一个定语从句，在mooncakes后省略了that I came across our chemistry teacher.
