Based on the Chemical Abundances and Velocities of Stars in the Milky

Based on the chemical abundances and velocities of stars in the Milky Way's disk and halo,we can conclude that the protogalactic fragments that came together to form the galaxy merged when the fragments had

A) not yet formed stars.
B) converted most of their gas into stars.
C) begun forming stars.
D) each formed a supermassive black hole at their center.