Here is how I approached the question. Since the charge density on the two sphere are of opposite polarity therefore, electric field is zero in the mid way. This implies A is correct. Above and below the mid way line, magnitude of electric field is constant. This implies C is correct. As C is correct therefore, B is also correct.
But the answers according to the book are C and D.
I assumed the spheres are partially kept one over other and overlapping region is referred in the question.
Please help me to improve my concepts and solve the question.