题目

This kind of wine is made in Holland and it has been kept for 13 years．So it _______special． A．hears                      B．looks                      C．sounds                   D．tastes 答案：D某人用平行于斜面的拉力，把一个重为1000N的物体，沿着长5m、高1m的斜面由底端匀速拉到顶端，拉力的大小为250N，则拉力所做的有用功为    J，此斜面的机械效率为    ，物体所受斜面的摩擦力为    N．