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': 'Dynamic response is due to: \nSelect and explain. \nA. Primary ending, B. Secondary ending, C. Tertiary ending, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]