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: Physiology
[{'content': "What are 'G-proteins'? \nSelect and explain. \nA. Membrane receptors, B. Membrane regulators, C. Second messengers, D. Membrane channels", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]