Do you know the reason she has changed her mind?A. for thatB. whichC. whyD. of which

问题补充：

Do you know the reason she has changed her mind?

A. for that

B. which

C. why

D. of which

答案：

A. for that

B. which

(答案→)C. why

D. of which

解析：考查定语从句;先行词是the reason，定语从句中缺少原因状语，用why引导定语从句，句意：你知道她改变主意的原因吗？