单选题 The reason ______ they died was lack of medical care.
A. which B. at which C. in which D. why

【正确答案】 D
【答案解析】本题考查的是reason作先行词时的定语从句。基本结构是the reasonwhy…is…，这里的why是关系副词；或者是the reason for which…is…，这里是介词+which引导的定语从句。所以选D。本句的意思是：“他们的死因在于缺少医疗护理。”