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 are classified according to: 
Select and explain. 
A. Action on substrate, B. Action of coenzymes, C. Nature of the enzymes, D. All of the above
A: Action on substrate
Answer: A: Action on substrate 
Explanation: None