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
[{'content': 'In human body, methionine is synthesized from ? \nSelect and explain. \nA. Cysteine, B. Proline, C. Threonine, D. None', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., None Methionine is an essential amino acid, cannot be synthesized in body.", 'role': 'assistant'}]