As a marble rolls across the floor, it gradually slows to a stop due to friction. Which statement best describes the change in mechanical energy of this system?
a.) Mechanical energy was transferred from the floor to the marble.

b.) Mechanical energy was transferred from the marble to the floor.

c.) The total energy of the marble and floor, including the mechanical energy, was reduced to zero.

d.) The mechanical energy of the marble was transformed into nonmechanical energy.