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 Krebs cycle, which of the following catalyses the step in which the first CO2 is released? \nSelect and explain. \nA. Aconitase, B. Isocitrate dehydrogenase, C. Succinate thiokinase, D. Succinate dehydrogenase', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]