A:逐渐变大
B:逐渐变小
C:大小不变
D:靠近穿衣镜
分别用如图所示的两个滑轮组,将同一物体提升到相同高度.若物体受到的重力为100N,动滑轮的重力为20N,在把物体匀速提升1m的过程中.(不计绳重和摩擦)下列说法不正确的是( )
— Did you hear the news about the fire in our building?
— Yes. It took the firemen two hours to_______ the fire.