题目

The riversuch heavy pollution already, it may now be too late to clean it up. A. has suffered             B. has happened C. has offered                  D. has filled 答案：【解析】选A。考查动词词义辨析。句意:这条河已遭受严重污染, 现在要想将它清理干净可能已太晚了。suffer遭受; happen发生; offer提供; fill充满。先化简，再求值：(x+1x-x+2x-1)÷4x2+2xx2-2x+1，其中x满足方程xx-1-2x=1．