Why Are Supermassive Black Holes Believed to Be Located at the Centre

Multiple Choice

Why are supermassive black holes believed to be located at the centre of many galaxies?

A) because the rotation curve of the galaxy indicates that 90% of the galaxy is dark matter
B) because the orbital motion of material near the centre is very fast and indicates a very massive core
C) because the shape of the bulge in all spiral galaxies can only be supported by a supermassive black hole
D) because the spiral structure requires a black hole to maintain the spiral arms