Selecting a mobile phone is no easy task because technology_______ so rapidly.
A:has changed
B:is changing
C:will have changed
D:will changed
下列语句中没有语病的一句是( )
重力为50牛的正方体金属块、底面积为0.01米2,放在面积为0.4米2的水平桌面上,则金属块对桌面的压强 ( )