The answer is the last option, which is: The foundation may be a rectangle:
The explanation for this problem is shown below:
1- A rectangle is defined as a parallelogram whose opposite sides are parallel and congruent. Its interior angles are right angles.
2- Keeping the definition above on mind, the diagonal of a rectangle divides it into to right triangles. So, we can verify if the shape of the frame is a rectangle by using the Pythagorean Theorem, which is:
Where is the hypotenuse (the measure of the diagonal) and
and
are the other sides of the right triangle.
3- Therefore, you have that must be equal to
to conclude that it is a rectangle:
4-So, as you can see, the answer is the option mentioned before.