The answer is the third option, which is: Trapezoid.
The explanation for this asnwer is shown below:
1- A rectangular pyramid is a solid whose base is a rectangle and its faces are triangles.
2- When you slice or cut a solid with a plane, you obtain a shape which is known as "Cross section".
3- In this case, if these plane is perpendicular to the base but does not pass through the top vertex of the rectangular pyramid, the intersection of the plane with the pyramid, or the resulting shape will be a trapezoid.
