A:cheer them u
B:join them u
C:add them u
D:pick them u
如图所示A、B两个正方体物体叠放在水平地面上,已知两物体的边长之比是2:1,密度之比为3:2,A与B的质量之比为____,B对A的压强与A对地面的压强之比为____.
铅蓄电池的电动势为2V,这表示( )