3×15=15，所以3和5是因数，15是倍数．______．
由分析知：3×15=15，只能说3和5是15的因数，15是3和5的倍数；
故答案为：错误．
You had better ________ some time every day for sports so that you can keep yourself energetic.(2012·福建)
A．set aside
B．take up
C．put away
D．give out
煤气回火的原因是什么？
