CE Four lightweight, plastic spheres, labeled $A, B, C,$ and $D,$ are
suspended from threads in various combinations, as illustrated in
FlGURE $19-47 .$ It is given that the net charge on sphere $D$ is $+Q$ , and
that the other spheres have net charges of $+Q,-Q,$ or $0 .$ From
the results of the four experiments shown in Figure $19-47,$ and the
fact that the spheres have equal masses, determine the net charge
of (a) sphere $A,(b)$ sphere $B,$ and $(c)$ sphere $C$ .