Answer: B) A machine that is 100% efficient
Explanation:
The second law of thermodynamics states that a machine will always be less than 100% efficient as heat is never converted completely into mechanical energy. Even an ideal, frictionless engine can't convert anywhere near 100% of its input heat into work.
Second law of thermodynamics states that any natural system tends to disorder. That is, the total entropy of the universe will tend to increase over time. Heat will alwyas from a hotter body to a colder body.
