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 TCA cycle of tricarboxylic acid, which is first formed \nSelect and explain. \nA. Isocitrate, B. Citrate, C. Succinate, D. Fumarate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Citrate', 'role': 'assistant'}]