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': 'Human beings, during synthesis of fatty acids cannot introduce double bonds beyond the position: \nSelect and explain. \nA. 4, B. 7, C. 9, D. 11', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Higher animals have d4, d5, d6, and d9 desaturases but cannot inse new double bonds beyond the 9 position of fatty acids. Thus, the essential fatty acids linoleic (6) and -linolenic (3) must be obtained from the diet. Ref: Harper 28thedition, chapter 23.', 'role': 'assistant'}]