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

The school has developed an online system students can choose their own teachers.
A. which
B. that
C. whom
D. where

A. whichB. thatC. whom(答案→)D. where解析：考察定语从句。定语从句是高考从句中必考的语法，在阅读文章中出现的频率也很高。关键在于分析句子结构，定语从句中如果既不缺主语，也不缺宾语和表语，就要考虑是否用关系副词或whose作定语，意为“谁的”。至于如何判断缺不缺主或是宾语，尤其是缺宾语的情况，要将先行词带到定从中谓语动词之后看是否符合逻辑搭配，如符合则缺宾语，如不符合就不缺。本题定语从句的现行词是online system,后面的定语从句主语是students，谓语动词是can choose后面的宾语是their own teachers。句子结构是完整的，故使用关系副词在句子做状语。D正确。

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