Which of the claims I to IV about the second law of thermodynamics, Carnot engines and the nature of heat are correct?

• I. Heat cannot be drawn from a single reservoir and turned entirely into work as the only outcome of any process.
• II. Heat cannot pass from a colder body to a hotter body as the only outcome of any process.
• III. A Carnot engine working between two given temperatures can reach 100% efficiency if all friction is removed.
• IV. Heat is a thermodynamic state variable.