What is the Carnot cycle?

I- The Carnot cycle is the ideal cycle for a thermal machine.
II- Carnot demonstrated that the maximum efficiency of any machine depends on the difference between the maximum and minimum temperatures reached during a cycle.
III- The Carnot cycle consists of four steps: isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression.
IV- The Carnot cycle is a real cycle that can be achieved by a thermal machine.
a) Only I and II are correct.
b) Only II and III are correct.
c) Only III and IV are correct.
d) I, II and III are correct.
e) I, II, III and IV are correct.