A:南北回归线
B:南北极圈
C:赤道
D:两极
— Sorry. I returned it to the library just now. Maybe it is still ____.
分别用如图所示的甲、乙两个滑轮组,在5s内将重为100N的物体G匀速提升2m,每个滑轮的重均为10N.不计绳重及摩擦,此过程中( )
____个