Answer:
A. rectangle, not a square.
Explanation:
A right rectangular prism is a shape of a cube which is made up of 6 rectangular edges.
It has 4 vertical edges and 2 horizontal edges
The adjacent edges of the rectangular prism is at right angles
A plane intersects a right rectangular prism parallel to its base that is the parallel edges. The cross section formed by the plane would be the shape of the base as it is parallel to base and will intersect the the 4 vertical edges perpendicularly.
Thus, the shape of the cross section formed by the plane would be best described by a rectangle and not a square because the base is in the shape of a rectangle.
The figure representing the plane is shown below.