9. According to the First Law of Thermodynamics, if a closed system absorbs heat Q from its surroundings and does work W on its surroundings, what is the change in the internal energy of the system, ΔU? (Sign convention: heat absorbed is positive, work done by the system is positive) (A) ΔU = Q + W (B) ΔU = Q - W (C) ΔU = W - Q (D) ΔU = -Q - W