Not until all the fish died in the river, _______ how serious the pollution is.       [ ]

A. did the villagers realize                

B. the villagers realize        

C. the villagers did realize                

D. didn't the villagers realize

如图所示的修枝剪刀把的末端，便可以轻松地剪断树枝．这时修枝剪刀属于_____杠杆，它的支点在______点．使用时，若在轴上加润滑油，则可以提高杠杆的 ______。