1. The problem asks which solid, when cut by a plane parallel to its base, produces a rectangular cross section. 2. Important rule: A plane parallel to the base of a solid will produce a cross section similar in shape to the base. 3. Analyze each solid: - Shape A: Sphere. Any cross section of a sphere is a circle, never a rectangle. - Shape B: Rectangular prism (cuboid). The base is a rectangle, so a plane parallel to the base will produce a rectangular cross section. - Shape C: Triangular prism. The base is a triangle, so the cross section parallel to the base is a triangle, not a rectangle. - Shape D: Cylinder. The base is a circle, so the cross section parallel to the base is a circle, not a rectangle. 4. Conclusion: Only the rectangular prism (Shape B) produces a rectangular cross section when cut by a plane parallel to its base.