Here's a problem to solve: Helena investigates how enzymes are important to body processes. How is the role of enzymes in biochemical activity best explained?

Among the 4 following options, which is the correct answer?

- A: Enzymes work at all pH levels.
 
- B: Enzymes decrease the rate of metabolism.
 
- C: Enzymes enable reactions to occur at lower temperatures.
 
- D: Enzymes raise the activation energy needed for a reaction.
 