In 1980 he caught a serious illess from whose effect he stil

In 1980 he caught a serious illess from whose effect he still suffers
为什么用from whose 不用which 这里是定语从句吗 那它的先行词是什么

这里先行词是illness,楼主少写了一个字母哟^_^
要看定语从句的先行词是什么,先把从句还原就可以了.
这里句子可以分成两个：In 1980 he caught a serious illness.
he still suffers from its effects.
意思是说：他仍饱受那场病痛之苦,所以这里it是指illness,所以,先行词就是illness,这里要用连接词就不能用which而要用whose,因为还原后是its,是一个所有格结构,所以连接词也要用所有格结构.