答案:B
楼主要理解句子的结构和whom/whose的用法.
1.关系代词whom代指先行词Granpa Liu,并代入定语从句中,为:
for (whom) life was hard in the past
= life was hard in the past for (whom)
= life was hard in the past for (Grandpa Liu)
对于刘爷爷来说,过去的生活非常艰苦
2.如果用whose,则whose = Grandpa Liu's,将其代入定语从句中后,句子明显有误
除非定语从句改成:whose life was hard in the past
即:(whose) life was hard in the past
= (Grandpa Liu's) life was hard in the past
过去刘爷爷的生活非常艰苦