In a heat engine, the work output per cycle Wcycle equals the net heat flow to the engine per cycle Qcycle QH-IQcl because of which of the following principles? (Mark all that apply.) OA. The 1st Law of Thermodynamics OB. The internal energy of the working substance is a state variable. ■ C. The definition of efficiency e-wcydeQH ■ D. The Ideal Gas Law pV = nRT E. NONE of the other choices.