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