题目内容

20．Cancer is a disease ___causes are still not clearly known．（　　）
A．whoseB．whichC．thatD．who

分析 癌症这种疾病的起因现在仍然不清楚．

解答 答案：A
题干中causes are still not clearly known是修饰disease的一个定语从句；从句中主语causes缺少表示所属关系的限定词，要用whose来连接．故选A．

点评 定语从句是一类比较重要的复合句．定语从句关系词的选择要根据从句的结构来确定，从句如果缺少主语或宾语，要用关系代词；从句结构如果完整，要用关系副词．学习时，要注意区分和掌握．

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