Astronomers Have Established That Quasars and Active Galaxies Have a Lot

Astronomers have established that quasars and active galaxies have a lot of mass at their centers in a very small volume of space. Why can't this mass be in the form of a cluster of stars that are quite close to each other?

A) all the clusters of stars are at the outer edges of galaxies; we have never seen any clusters of stars toward the middle of galaxies
B) things at the centers of galaxies all move so fast, the stars in the cluster would be launched outward and would never remain at the center
C) to fit as much matter into the cluster as we observe, the stars in the cluster must be so close to each other they would merge into a superstar and soon collapse into a black hole
D) we could easily observe such a star cluster in distant galaxies, and we don't see them
E) none of the above