31- Which of the following statements best expresses the main idea of the passage?
A. Bailin began studying the Sagittarius Dwarf when he was a graduate student in astronomy.
B.The gravitational tidal forces of the Milky Way are destroying the Sagittarius Dwarf.
C.Most astronomers have come to an agreement that evidence about how galaxies have formed is, at best, circumstantial.
D.Evidence suggests that the warp in the Milky Way’s disk results from the Milky Way’s interaction with a small satellite galaxy.