Why Does the Temperature of the Gas Between Galaxies in Galaxy

Why does the temperature of the gas between galaxies in galaxy clusters tell us about the mass of the cluster?

A) The temperature is always directly related to mass,which is why massive objects are always hotter than less massive objects.
B) The temperature tells us the average speeds of the gas particles,which are held in the cluster by gravity,so we can use these speeds to determine the cluster mass.
C) The temperature of the gas tells us the gas density,so we can use the density to determine the cluster's mass.
D) The question is nonsense-gas temperature cannot possibly tell us anything about mass.