A:m1>m2
B:f1<f2
C:
D:以上说法均不对
at the time, a pack of, help out, in the meantime, be terrified of, yell out, sort out, ahead of, aim at, in time
将一长方体放在水平桌面上,如右图所示,若沿虚线切掉上部分,则剩下部分的密度、对桌面的压强、压力变化是( )
胎生对于其他的生殖方式的优势是( )