— Can you talk with me _________ the phone?
— Yes, but not now.
A:by
B:with
C:on
D:in
有些真菌可以产生能杀死某些致病细菌的物质,这类物质称为( )
甲、乙两物体都做匀速圆周运动,其质量之比为1:2,转动半径之比为1:2,在相等时间里甲转过60°,乙转过45°,则它们所受外力的合力之比为( )