The law of universal gravitation states that a gravitational force exists between all objects in the universe. This force is directly proportional to the masses of the two objects and inversely proportional to the distance between them. This principle is a law because
A.
it cannot be tested through a controlled scientific investigation.
B.
it is subject to change as new technology and evidence emerges.
C.
it is contradictory to ideas proposed by other scientists.
D.
it has been demonstrated to be without exception under certain stated conditions