Which of the following may suggest a catalyst has been used in a reaction, given the energy diagram for the same reaction without a catalyst?

When comparing the energy diagram for an uncatalyzed reaction and catalyzed reaction, the prominent difference is the difference in the height of the peak of the energy diagram. The height of this peak represents the activation energy of the reaction, and catalysts provide alternate reaction pathways to reduce this energy. Thus, the height of the peak is reduced.