Which of the Following Situations Would Be Allowed by the Second

Which of the following situations would be allowed by the second law of thermodynamics?

A) running of a heat engine using temperature differences in the oceans
B) converting 100 joules of heat energy into 100 joules of work
C) passage of heat from the freezer into the refrigerator section
D) the reduction of waste heat from a power plant to zero with better technology