Why Are Supermassive Galaxies Often Found at the Cores of Rich

Multiple Choice

Why are supermassive galaxies often found at the cores of rich galaxy clusters?

A) Most of the matter forming the cluster fell into the center to form one large galaxy.
B) They are the result of many galactic mergers; one galaxy growing at the expense of others.
C) Such a large galaxy attracted smaller galaxies around it to form a cluster.
D) Large galaxies, passing a cluster, get captured into the center.
E) Many globular clusters swarmed together to form it.