One Curious Fact About the Milky Way Galaxy, Discovered in the Past

Multiple Choice

One curious fact about the Milky Way Galaxy, discovered in the past two decades, is that

A) a significant fraction of its mass is in the form of globular clusters, distributed in a spherical halo centered on the galactic center.
B) a large black hole is slowly clearing out the mass near the galactic center, leaving a cold, dark void.
C) enormous amounts of energy are pouring out of a compact but very massive source at its center.
D) most of its mass is in the spiral arms extending out into space.