Which of the following can be the base of a pyramid?

Option (a) cannot be the base of a pyramid because pyramid is a polyhedron and its base is polygon.

(b) Circle cannot be the base of a pyramid because pyramid is a polyhedron and its base is polygon.

(c) Octagon can be the base of a pyramid because it has a polygon as a base and lateral faces are triangle.

(d) Oval cannot be the base of a pyramid because pyramid is a polyhedron and its base is polygon