This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Enzymes increase reaction rates by 
Select and explain. 
A. Altering the free energy of the action, B. Inhibiting the backward reaction, C. Enhancing the forward reaction, D. Decreasing the energy of activation
D: Decreasing the energy of activation
Answer: D: Decreasing the energy of activation 
Explanation: MECHANISM OF ENZYME ACTION
Explained by different theories:

Lowering of activation energy
Michaelis-Menten theory
Fischer’s Template theory
Koshland’s Induced Fit theory.

Lowering of Activation Energy
Enzymes lower the activation energy. Activation energy is defined as the energy required to convert all molecules of a reacting substance from ground state to transition state.