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: Medicine
[{'content': 'Orthostatic hypotension is said to be present, if systolic blood pressure falls by_____while assuming standing posture from sitting posture. \nSelect and explain. \nA. >10 mm Hg, B. >20 mm Hg, C. >30 mm Hg, D. >40 mm Hg', 'role': 'user'}, {'content': "Answer: B \nExplanation: Orthostatic hypotension is deﬁned by a fall in systolic pressure > 20 mmHg or in diastolic pressure > 10\xa0 mmHg in response to assumption of the upright posture from a supine position within 3 min. There\xa0 may also be a lack of a compensatory tachycardia, an abnormal response that suggests autonomic\xa0 insuﬃciency, as may be seen in patients with diabetes or Parkinson's disease. Orthostatic hypotension\xa0 is a common cause of postural lightheadedness/syncope and should be assessed routinely in patients\xa0 for whom this diagnosis might pertain.\nReference: : Harrison’s medicine page no\xa0 126", 'role': 'assistant'}]