What Evidence Suggests That the Protogalactic Cloud That Formed the Milky

What evidence suggests that the protogalactic cloud that formed the Milky Way resulted from several collisions among smaller clouds?

A) The stars in the halo of the Milky Way are organized into several dense clusters arranged throughout the halo.
B) The Milky Way resembles an elliptical galaxy more than other spirals do.
C) Halo stars differ in age and heavy-element content, but these variations do not seem to depend on the stars' distance from the galactic center.
D) The bulge of the Milky Way is surrounded by many globular clusters, just as elliptical galaxies are.
E) The Milky Way is the central galaxy of a dense cluster of galaxies.