17. Which is correct?
(A) When the concentrations of the reactants and products of a given chemical reaction remain unchanged, the system is at chemical equilibrium.
(B) There are infinite equilibrium positions at equilibrium.
(C) For an endothermic reaction, the reaction will shift to right when decreasing temperature.
(D) In exothermic reactions, the reactants have lower potential energy than the products.
(E) An exothermic reaction usually occurs more quickly than an endothermic reaction.