When he was working there he caught a serious illness from efforts he still suffers.
A. which
B. that
C. whose
D. what
网友回答
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。