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 potential is: \nSelect and explain. \nA. Decremental phenomenon, B. Doesn't obey all or none phenomenon, C. K+ goes from ECF to ICF, D. Threshold stimulus is required", 'role': 'user'}, {'content': 'Answer: D \nExplanation: D i.e. Threshold stimulus is required', 'role': 'assistant'}]