A:30°
B:45°
C:65°
D:75°
— Can we eat much sugar?
— No, Too much sugar your teeth.
My father's grandfather who was famous in my hometown ________ the hospital in 1923.
真空中有两个点电荷相隔一定距离r,相互作用力为F。若其中一个电荷的电量变为原来的4倍,为要保持原来的作用力大小不变,则两个电荷间的距离变为原来的多少倍( )