A:get, get
B:getting, getting
C:getting, get
D:get, getting
— It was ___________ who helped us out of danger.— What brave and helpful children! We should learn from them.
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: