is known to us all is that the old worker life was hard in the past still works hard in

问题补充：

is known to us all is that the old worker, life was hard in the past, still works hard in his seventies.

A. As, whom

B. What, whom

C. It, whose

D. What, whose

答案：

A. As, whom

B. What, whom

C. It, whose

D. What, whose

解析：考查主语从句和非限制性定语从句，第一空是what引导的主语从句，在主语从句中what做的是主语，第二空是非限制性定语从句，先行词是the old worker，定语从句中缺少定语，用whose引导定语从句，句意：众所周知的是那个过去生活很艰难的老工人70岁了还很辛苦工作。选D。