用图3甲、乙两种方式匀速提升重为100N的物体,已知滑轮重20N、绳重和摩擦力不计.则() A . 手的拉力:F甲=F乙;机械效率:η甲=η乙 B . 手的拉力:F甲<F乙;机械效率:η甲<η乙 C . 手的拉力:F甲>F乙;机械效率:η甲<η乙 D . 手的拉力:F甲>F乙;机械效率:η甲>η乙 答案:D—How can I get to Guangzhou within five hours? —There is no way by air. A.rather than B.other than C.more than D.less than