It has a negative slope, so B and C are eliminated. The graph also has a solid line instead of a dashed line. This means D is eliminated because it is only greater than. If the graph had a dashed line, then D would be correct, but it does not.
To see if the lengths make a triangle, use the Pythagorean theorem. Insert the biggest value as c (the hypotenuse, which is always the longest side in a right triangle). If both sides equal each other, it is a right triangle: