. _____ is known to us is that the old doctor, for _____ life was hard in the past, still works very hard in his late life.
A. As; whom
B. What; whom
C. It; whose
D. As; whose
答案：B
翻译：我们都知道：那位老医生，尽管他过去的生活非常艰苦，但他在晚年还是非常辛苦地工作。
解释：
分析句子结构可知：主句主语是一个从句 ____ is known to us，主句谓语是一个系表结构，其中系动词is，而表语又是一个从句 that the old doctor still works very hard in his late life.
该主语从句 _____ is known to us中，缺少一个表示sth的主语，所以必须用what代替并引导该从句。
而表语从句中又含有一个非限制性定语从句 for _____ life was hard in the past，它修饰先行词the old doctor.
将先行词代入定语从句，只能变化为：
life was hard (for the old doctor) in the past
= life was hard (for whom) in the past
= (for whom) life was hard in the past.
由此可知只有答案B为正解。