In a right rectangular pyramid with four equal edges, each triangular face is isosceles, and the top of the pyramid is directly above the center of the base. When a slice is made parallel to the base, the resulting cross section will be a shape similar to the base.
Since the base of the pyramid is a rectangle and the slice is parallel to the base, the cross section will also be a rectangle. However, since you have provided specific options and if you meant to include a square option, it seems that the question is suggesting that the edges must be equal in length.
Assuming the base is square due to the mention of "equal edges," then the answer would be a square.
So, if the base of the pyramid is a square (which is consistent with having equal edges), the cross section would indeed be a square.