Which statement explains the Pythagorean Theorem?
A: If the interior angles of a triangle add to 180 degrees, then the sum of the legs of the triangle is equal to the square of the hypotenuse.
B: If all angles in a triangle are equal measure, then the length of all sides will be equal.
C: If a triangle is a right triangle, then sum of the squares of the legs is equal to the square of the hypotenuse.
D: If a triangle is a right triangle, then the sum of the squares of the longest leg and the hypotenuse is equal to the square of the third side.