A:①②④
B:①③④
C:①②③
D:②③④
— Do you know our new manager?
— Yes. He to be a friend of my brother's.
如图所示,斜面高为1m,长为4m,用沿斜面向上大小为75N的拉力,将200N重的木箱由斜面底端缓慢匀速拉到倒顶端,用时0.5min。求: