The MOST Important Reason Globular Clusters Are Useful for Finding

The MOST important reason globular clusters are useful for finding the speed of the Sun in its orbit around the Milky Way is that:

A) globular clusters are bright and easily seen at large distances.
B) globular clusters on average rotate at the same speed as the Sun around the center of the Galaxy.
C) globular clusters are distributed uniformly around the Galaxy.
D) the average velocity of all the globular clusters must be zero if the globulars are to maintain their orbits around the galactic center.