Explanation: The temperature of a substance cannot increase during phase change, so both A and B cannot happen simultaneously. And internal energy is the sum of the microscopic potential and kinetic energies of a substance, which increase with temperature and phase transition.
Assuming that the water and steel are into an <em>adiabatic calorimeter</em> (there's no heat transferred to the enviroment), the temperature of both is identical when the system gets to the equilibrium