The base of a cone is a circle.
Here's why:
1. A cone is a three-dimensional shape that has a circular base and narrows to a point called the apex.
2. The circular base of the cone provides stability and support for the cone's structure.
3. The shape of the base determines the properties of the cone, such as its surface area and volume.
4. In contrast, shapes like a triangle, square, or pentagon do not have the roundness needed to form the base of a cone.
Therefore, the correct answer to the question is C. Circle.
