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: Surgery
[{'content': 'In CPR, chest compressions are done: \nSelect and explain. \nA. On the upper part of sternum, B. On the xlphisterum, C. On the middle of the lower part of the sternum, D. On the left side of the chest', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]