Answer: The first box is circle and second box is rectangle.
Explanation:
If you are asking about the shape of the cross section for a right circular cylinder, that is the case. A parabola or triangle can't be sliced so the cross section is parallel or perpendicular to the base.
If the cross section is parallel to the base, it is a circle.
If the cross section is perpendicular to the base, it is a rectangle.