This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fatty acid and synthesis, Subject name: Biochemistry
[{'content': 'Conversion of stearic acid to oleic acid is catalysed by: \nSelect and explain. \nA. D3desaturase, B. D6desaturase, C. D9desaturase, D. D12desaturase', 'role': 'user'}, {'content': "Answer: C \nExplanation: Desaturase enzymes can't introduce double bonds beyond the D9 position. This is why ceain fatty acids are essential and must be taken in diet.", 'role': 'assistant'}]