What Evidence Supports the Existence of a Black Hole at the Center

Multiple Choice

What evidence supports the existence of a black hole at the center of our galaxy?

A) The motions of the gas and stars at the center indicate that it contains 4 million solar masses within a region only 3 light- years across.
B) We can see gas falling into an accretion disk and past the event horizon of a black hole.
C) We observe a large, dark object that absorbs all light at the center of our galaxy.
D) We observe an extremely bright X- ray source at the center of our galaxy.
E) All of the above