The school has developed an online systemstudents can choose their own teachers.A. whichB

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A. which
B. that
C. whom
(答案→)D. where
解析：考查定语从句：句意：学校已经开发了一个在线系统，里面学生可以选择自己的老师。这是定语从句，先行词是an online system，定语从句中缺少的是地点状语，选D。