Final answer:
Enzymes decrease the activation energy required for a reaction, resulting in a decrease in reaction rate.
Step-by-step explanation:
An enzyme catalyzes a reaction by lowering the activation energy required for the reaction to occur. This means that option A - increase in activation energy is incorrect. The correct answer would be option C - decrease in reaction rate. Enzymes can also increase the reaction rate by speeding up the formation of the product. As for option D - shift in equilibrium, enzymes do not affect the equilibrium position of a reaction. They only accelerate the rate at which equilibrium is reached.