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': 'Action of a - subunit of G protein is: \nSelect and explain. \nA. Breakdown of GTP to GDP, B. Conversion of GDP to GTP, C. Internalization of receptors, D. Binding of agonist', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. Breakdown of GTP to GDP', 'role': 'assistant'}]