What evidence supports the idea that a collision between two spiral galaxies might lead to the creation of a single elliptical galaxy? A) observations of some elliptical galaxies surrounded by shells of stars that probably formed from stars stripped out of smaller galaxies B) the fact that elliptical galaxies dominate the galaxy populations at the cores of dense clusters of galaxies C) observations of some elliptical galaxies with stars and gas clouds in their cores that orbit differently from the other stars in the galaxy D) observations of giant elliptical galaxies at the center of dense clusters that may have grown by consuming other galaxies E) all of the above