A plane intersects a prism to form a cross section that is a polygon with five sides. What is the minimum number of sides that the polygon at the base of the prism must have?

A. 3

B. 4

C. 5

D. 6

E. 7

The answer is 4. Obviously, 5 would work if you just slice across the prism, and there's no way you can have a prism with a 2-sided base. It must be then less than 5, either 3 or 4. 5 sides is not also possible upon drawing. I can get a rectangular prism to have a 5-sided cross section if you cut near one corner of the base and then exit along the opposite edge.