In a right rectangular pyramid with four equal edges, if you make a slice parallel to the base, the cross-section will be similar in shape to the base. Since the base of a right rectangular pyramid is a rectangle, the cross-section will also be a rectangle.
However, since you selected "square" (B) and the shape of the base can be square if specified or a rectangle, if that base is a square, then your answer is correct.
But if the base is not explicitly defined as a square, the appropriate answer should be noted as "rectangle" (not given in your options) or if it's implied the equal edges somehow indicate a square shape (like in the case of a square base pyramid), wouldn't be a square always if unequal dimensions were in play.
In summary, if the pyramid has a square base, then your answer would be correct as "square." Otherwise, that's a clarification needed.
Overall, "trapezoid" would be a possible answer in scenarios involving non-parallel bases or differing side lengths but it looks like that wouldn't apply here.