Which type of figure has only one base?

A - Prism
B - Sphere
C - Cylinder
D - Pyramid

To determine which type of figure has only one base, we need to understand the characteristics of each option:

A - Prism: A prism is a three-dimensional figure that has two congruent and parallel bases. Therefore, it does not have only one base.

B - Sphere: A sphere is a three-dimensional figure with no edges or vertices. It does not have a base.

C - Cylinder: A cylinder is a three-dimensional figure with two congruent circular bases that are parallel to each other. Since it has two bases, it does not have only one base.

D - Pyramid: A pyramid is a three-dimensional figure that has one base and triangular faces that meet at a common vertex. This means that it has only one base.

So, the correct option is D - Pyramid.