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
[{'content': "Casal's necklace is seen in deficiency of: September 2012 \nSelect and explain. \nA. Vitamin A deficiency, B. Niacin, C. Vitamin B12 deficiency, D. Iron deficiency anemia", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans: B i.e. Niacin The Casal collar or Casal necklace is a clinical sign in which there is erythematous pigmented skin rash in the distribution of a broad collar (dermatomes C3 and C4). It is seen in patients with pellagra.', 'role': 'assistant'}]