Answer:
A. Some work input is used to overcome friction.
Explanation:
As we know that in real conditions it is not possible to form a surface which do not have any friction or we can say that it is not possible to have a surface which is 100% smooth
So here when a machine absorbs some energy as its input work then some part of this energy is used against frictional force between its moving part and hence the output energy is less than the energy that it absorb.
So output energy is never same as the input energy of a machine.
So correct answer would be
A. Some work input is used to overcome friction.
