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': 'The most common cause of hypovolemic shock is \nSelect and explain. \nA. Haemorrhage, B. Decreased RBC formation, C. Bone marrow suppression, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]