Answer:
B. a rectangle
Step-by-step explanation:
When a figure is sliced along a given or required plane, the cross section of the sliced surface produces another figure or shape.
In the question, the figure has a triangular base. So that, the cross section along the required plane would give a rectangular shape. This is because the cross section is perpendicular to the triangular base, and passes through a vertex of the base.
By appropriate procedures and the given conditions, the shape of the cross section would be a rectangle.
