Scientists believe the scarps on Mercury formed as a result of which process?

A. plate tectonics

B. volcanic eruptions

C. bombardment by asteroids

D. shrinking of the planet as it cooled

Looks like the answer is B

But I am not sure, could be A, I know planets don't shrink when they are cold and unless the asteroid has mercury or mercury is on the planet already and the asteroid pierces it, it is not C.