In which pictured region (if any) in the diagram below could the electric field possibly be zero (excluding points at infinite distance from the spheres)?
The diagram shows two spheres, charged uniformly as indicated. All regions are along a line connecting the centers of the objects.
Region $A$ is anywhere to the left of the positive charge. Region $B$ is to the right of the positive charge and closer to the positive charge than to the negative charge. Region $C$ is to the right of the positive charge but closer to the negative charge than to the positive charge. Region $D$ is anywhere to the right of the negative charge.