Which of the following best states the Clausius statement of the Second Law of Thermodynamics?
a) The entropy of an isolated system always increases in a spontaneous process.
b) No heat engine can convert all the heat supplied to it into work in a cyclic process.
c) Heat cannot of itself flow from a colder body to a hotter body without the aid of external work.
d) Heat cannot of itself flow from a hotter body to a colder body without the aid of external work.