This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Enzymes, Subject name: Biochemistry
Cofactor of carbonic anhydrase is 
Select and explain. 
A. Molybdenum, B. Zinc, C. Copper, D. Selenium
B: Zinc
Answer: B: Zinc 
Explanation: The active site of most carbonic anhydrases contains a zinc ion; they are therefore classified as metalloenzymes. One of the functions of the enzyme in animals is to interconve carbon dioxide and bicarbonate to maintain acid-base balance in blood and other tissues and to help transpo carbon dioxide out of tissues.