题目

_________ 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．As; whose         D．What; whose 答案：B先化简分式，再从-1、0、1、2、3这五个数据中选一个合适的数作为x的值代入求值．