In a practical machine, the power output is smaller than the power input. Considering the law of energy conservation, what can explain this occurrence?

A. Some of the energy going into the machine is being destroyed.
B. Some of the energy coming out of the machine is being destroyed.
C. Some of the energy is used to combat friction, and thus is transformed from mechanical energy to heat.
D. Some of the energy going into the machine is being created at a quicker rate than the energy coming out is being destroyed.