Identify the diagram that best represents the relationship among the given classes:
Human being, Doctors, Post-graduates

Let's analyze the relationships among the three categories:
Both Doctors and Post-graduates are entirely part of the Human being category. Therefore, both circles must lie completely inside the larger circle of "Human beings".

Some Doctors can be Post-graduates (specialists with PG degrees), and some Post-graduates can be Doctors. Thus, the circles for Doctors and Post-graduates must partially intersect each other.

This relationship is represented by a large circle containing two intersecting circles inside it, which corresponds to option A.