18. _____is known to us all is that the old scientist, for____ life was hard in the past,still works very hard in his eighties.

A.     As; whom           B. What; whom          C. It; whose          D. As; whose

【解析】B本题考查连接代词。_____is known to us all 是主语从句，排除AD,第一个空上的词要做主语， 第二个空上的词做for的宾语，代替the old scientist。