Even If a Black Hole Emitted No Light, We Can

Multiple Choice

Even if a black hole emitted no light, we can still detect it:

A) from sound waves produced by material falling onto the black hole
B) by tides produced on the Earth's oceans
C) through its Hawking radiation
D) through its gravitational effect on surrounding gas or stars
E) by looking for dark patches on the sky where the black hole swallows background light