When two black holes spiral around each other and ultimately collide, they send out gravitational waves - ripples in space and time that can be detected with extremely sensitive instruments on Earth. ... If confirmed, it would be the first known light flare from a pair of colliding black holes.
The answer to your question is C.
Erosion, weathering, mechanical changes, chemical changes.
Really, any interaction can change the composition of a rock whether it be done by man or through nature.
125/5 = 25 meters per second
