A:to be living
B:to have lived
C:to have been lived
D:to live
用动力臂是阻力臂2倍的杠杆将重400N的货物抬高20cm,手向下压杠杆的力是220N,手下降的高度是____ cm,人做的总功是____ J,这根杠杆的机械效率是____.