Which of the following best defines thermal equilibrium between two bodies in contact?
(a) Both bodies contain the same total amount of thermal energy, regardless of temperature.
(b) Both bodies reach the same temperature, and no net transfer of energy as heat occurs between them.
(c) The hotter body continues to transfer energy to the cooler body at a constant rate.
(d) Both bodies have identical heat capacities, so their temperatures stop changing even while heat is exchanged.