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': '42 yrs old man presented with dizziness on standing,SBP falls by 50 mm Hg and HR is 52/min likely cause is -a)  CHFb)  Inferior wall MIc) Pheochromocytomad) Theophylline toxicitye) Sick sinus syndrome \nSelect and explain. \nA. ab, B. ad, C. be, D. ce', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]