如图所示，平行板电容器的电容为C，带电荷量为Q，板间距离为d，今在两板的中点处放一点电荷q，则它所受静电力的大小为

A．k

B．k　　

C．

D．

It is a paradox that in       a rich country there should be      many poor people.    [    ]

A. such; such      

B. such; so      

C. so; so      

D. so; such