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
Molybdenum is a constituent of: 
Select and explain. 
A. Xanthine oxidase, B. Cytochrome oxidase, C. Phosphofructokinase, D. Carbonic anhydrase
A: Xanthine oxidase
Answer: A: Xanthine oxidase 
Explanation: Molybdenum containing enzymes include aldehyde oxidase, sulfite oxidase and xanthine oxidase.