To determine which shape has a circular cross section when the cross section is taken parallel to the base, let's analyze the given shapes:
A. Cone: A cone has a circular base. When a cross section is taken parallel to its base, it will create a smaller circle that is parallel to and centered around the same central axis as the base.
B. Dodecahedron: A dodecahedron is a polyhedron with twelve flat faces, each of which is a regular pentagon. It does not have a circular cross section when cut parallel to any face.
C. Rectangular Prism: A rectangular prism has rectangular faces. When a cross section is taken parallel to its base, it will create a smaller rectangle, not a circle.
D. Octahedron: An octahedron has eight triangular faces. Similar to the dodecahedron, it does not have circular cross sections parallel to any of its triangular faces.
From this analysis, the shape that has a circular cross section when the cross section is taken parallel to the base is the cone. Thus, the best answer is:
A. Cone
