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
Cobalt forms a component of which vitamin 
Select and explain. 
A. Biotin, B. Vitamin B12, C. Vitamin A, D. Tocopherol
B: Vitamin B12
Answer: B: Vitamin B12 
Explanation: Vitamin B12 is a corrinoid, i.e. cobalt-containing compound possessing the corrin ring.