Given below is a diagram of three circles A, B & C inter-related with each…

Concept: In a class diagram, each circle stands for one class, and every labelled region stands for exactly one membership signature — the region belongs to every circle that encloses it and to no circle that leaves it out. A description of the form "X that are Y but are not Z" therefore picks out the single region that lies inside the X-circle and the Y-circle while lying outside the Z-circle.

Application: Here circle A is the class of Indians, circle B is the class of scientists and circle C is the class of politicians. The phrase "Indian scientists who are not politicians" imposes three conditions at once — inside A, inside B, and outside C. In the given drawing, the lens shared by circles A and B has two parts: the upper part that also lies inside C, and the lower part that lies outside C. The lower part is labelled s, so s is exactly the set of people who are Indian and scientists and not politicians. Hence the required code is s.

Cross-check: Each of the other labelled regions fails at least one of the three conditions:

• q lies inside all three circles, so every member of q is a politician; including q would violate the "not politicians" condition.

• p lies inside A and C but outside B — Indians who are politicians and are not scientists.

• r lies inside B and C but outside A — scientists who are politicians and are not Indians.

Every other code adds at least one of p, q or r to s, and each of those regions either brings in politicians or brings in people outside circle A. The region s alone meets inside-A, inside-B and outside-C together, so the required code is s.