This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
[{'content': 'VITAMIN WHICH IS NOT SYNTHESIZED BY THE BACTERIAL FLORA IN THE INESTINE IS? \nSelect and explain. \nA. vitamin k, B. Biotin, C. Niacin, D. Pantothenic acid', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Endogenously synthesized Vitamins are 1. Synthesized by the body- Niacin: synthesized from an amino acid Tryptophan Vitamin D: synthesized from 7 Dehydrocholesterol by exposure to UVB rays(290-315nm)in the skin. 2. Synthesized in the body(by Bacterial flora in the intestine) Vitamin K Biotin Pantothenic Acid Reference: Harpers illustrated biochemistry 30th edition', 'role': 'assistant'}]