Final answer:
The cross-section of a polygon with eight sides suggests the base of the corresponding prism also has 8 sides.
Step-by-step explanation:
When a plane intersects a prism parallel to one of the prism's sides, the resulting cross-section has the same shape and number of sides as the face it is parallel to. If the cross-section is a polygon with eight sides, known as an octagon, then it means that the base of the prism that the plane is parallel to also must have eight sides. Therefore, the base of the prism has 8 sides, which corresponds to option b. This question involves visualizing geometric shapes and understanding the properties of a prism and its cross-sectional slices.