A
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### Question:
Pepsin is an enzyme that acts in the stomach for protein digestion. Which of these is most likely the main role of pepsin in this metabolic reaction?

### Choices:
A. to speed up the rate of reaction
B. to reduce the loss of energy as heat
C. to control the direction of the reaction
D. to protect the reaction from other chemicals

### Answer:
