A:more than twice
B:as twice as many
C:twice as many a
D:more than twice as many
若f(x)=x3﹣3x+m有且只有一个零点,则实数m的取值范围是____
如图,已知⊙O1的半径为1cm,⊙O2的半径为2cm,将⊙O1,⊙O2放置在直线l上,如果⊙O1在直线l上任意滚动,那么圆心距O1O2的长不可能是( )