问题补充：
Safety in school has been of great concern (关注) because of recent reports about accidents students got injured or killed at school.
A. for which
B. when
C. which
D. in which
答案：
A. for which
B. when
C. which
(答案→)D. in which
解析：考查定语从句。句中先行词为accidents，在从句中作地点状语，故用关系词in which = where，选D。
