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': 'Physiological changes during severe exercises are all except \nSelect and explain. \nA. Hyperventilation in the beginning, B. Hyperkalemia, C. Decreased pa O2, D. Decreased pa CO2', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]