Which One of These Statements About Clusters of Galaxies Is

Multiple Choice

Which one of these statements about clusters of galaxies is true?

A) The observed mass of the galaxies of the cluster is many thousands of times too small to hold the cluster together.
B) The observed mass of the galaxies of the cluster is about 10 times larger than the amount needed to hold the cluster together.
C) The observed mass of the galaxies in the cluster is about 10 times too small to hold the cluster together.
D) The observed mass of the galaxies of the cluster is almost exactly equal to the mass needed to hold the cluster together.