According to A Black Hole Is NOT a Hole by Carolyn Cinami DeCristofano, astronomers think a supermassive black hole is created w
hen radio waves travel through space to Earth.
there is too much empty space in a galaxy.
gravity causes many, many stars to collide.
a single star or planet explodes and collapses.
I would say the answer is D, because when writing a summary you should probably include all of the things listed in the other options. Hope this helped!
