What the doctors really doubt is my mother will recover from the serious disease soon. A.

问题补充：

What the doctors really doubt is my mother will recover from the serious disease soon.

A. when

B. how

C. whether

D. why

答案：

A. when

B. how

(答案→)C. whether

D. why

解析：主要测试表语从句。此类试题的解决方法主要应该从所给答案以及句子 my mother will recover from the serious disease soon来分析可知选择whether最佳。译文：医生真正怀疑的是我母亲是否能够从严重的疾病中快点恢复。