Answer: A rectangle
Note: I am a bit confused between A), B), and C), but the answer I am going for is C).
Explanation:
By definition, a cross-section is the intersection of a plane and a body of three dimensions.
A pentagonal prism has a pentagon as its base. and its lateral faces are rectangles.
If a plane perpendicular cuts the pentagonal prism to the base, this means that the plane is parallel to lateral faces, then, the shape of the cross-section that is formed is also a rectangle.