A:convenient
B:excellent
C:valuable
I think watching table tennis match is ____ (simple) a waste of time. I have no interest in it.
体积相同的甲、乙两物体的质量之比是2:3,它们的密度之比 ____ ;如果把甲物截去一半,乙截去45,两物体剩余部分的密度之比是____
He wants __________ our classroom clean.