you are familiar with the principle of superposition as applied to the electric fields of a collection of point charges. we may apply this principle to extended charge distributions as well. for this problem, model each charged object as a collection of many individual charges, then use symmetry arguments in order to reason out your answer. for which configuration(s) does the total electric field vector at the origin have nonzero components in the x direction as well as the y direction (i.e., both x and y components are non-zero)?