When he was working there he caught a serious illness from efforts he still suffers. A. w

问题补充：

When he was working there he caught a serious illness from efforts he still suffers.

A. which

B. that

C. whose

D. what

答案：

A. which

B. that

(答案→)C. whose

D. what

解析：from whose efforts he still suffers 为修饰 a serious illness 的定语从句，whose 在定语从句中用作定语，修饰 efforts。