A hammer is used to drive a nail into a board. Work is done in the act of driving the nail. Compared to the moment before the hammer strikes the nail, the mechanical energy of the hammer after its impact will be:

A. Greater, because the hammer has done work.
B. Greater, because work has been done on the hammer.
C. Less, because the hammer has done work.
D. Less, because work has been done on the hammer.