Two Asteroids, of the Same Mass, Have a Gravitational Potential

Multiple Choice

Two asteroids, of the same mass, have a gravitational potential energy U. If a third asteroid, of the same mass, moves toward them, to a position such that the distances between the three asteroids are the same, the gravitational potential energy of the system will have changed by

A) 4U.
B) U.
C) 2U.
D) 3U.
E) 5U.