Two large thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs and of magnitude $16\times {10}^{-22}\mathrm{ }\mathrm{C} {\mathrm{m}}^{-2}$. The electric field between the plates is

The diagram shows the arrangement of three small uniformly charged spheres $A$, $B$ and $C$. The arrows indicate the direction of the electrostatic forces acting between the spheres (for example, the left arrow on sphere $A$ indicates the electrostatic force on sphere $A$ due to sphere $B$). At least two of the spheres are positively charged. Which sphere, if any, could be negatively charged?

Five Styrofoam balls are suspended from insulating threads. Several experiments are performed on the balls and the following observations are made,
(i) Ball $A$ repels $C$ and attracts $B$.
(ii) Ball $D$ attracts $B$ and has no effect on $E$.
(iii) A negatively charged rod attracts both $A$ and $E$.
An electrically neutral Styrofoam ball gets attracted if placed nearby a charged body due to induced charge. What are the charges, if any, on each ball?