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: Social & Preventive Medicine
True regarding vitamin B3 are all except: March 2012 
Select and explain. 
A. Tryptophan is a precursor, B. Milk is a rich source, C. Pellagra results due to deficiency, D. Not excreted in urine
B: Milk is a rich source
Answer: B: Milk is a rich source 
Explanation: Ans: B i.e. Milk is a rich source