Answer: Rectangle
Explanation:
A cylinder is a basic curved geometric shape, with 2 circular bases.
Its surface formed by the points at a fixed distance from a given line segment, which is known as the axis of the cylinder.
As the bases of cylinder are two identical circles which are perpendicular to the curved surface.
The curved surface when we open will be rectangle.
Therefore, a rectangle is the shape of the cross section taken perpendicular to the base of a cylinder.