Which of the following is the correct statement of the second law of thermodynamics?

A. There is a definite amount of mechanical energy, which can be obtained from a given quantity of heat energy

B. It is impossible to transfer heat from a body at a lower temperature to a higher temperature, without the aid of an external source

C. It is impossible to construct an engine working on a cyclic process, whose sole purpose is to convert heat energy into work

D. All of the above

Answer: Option D