The school has developed an on­line system students can choose their own teachers.A. w

问题补充：

The school has developed an on­line system students can choose their own teachers.

A. which

B. when

C. that

D. where

答案：

A. which

B. when

C. that

(答案→)D. where

解析：句意：学校研发了一个网络系统，在这一系统中学生可以选择自己的老师。这里是定语从句先行词是on­line system，where在从句中作地点状语，其他的关系词不能作地点状语，故选D。