This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abdomen and pelvis, Subject name: Anatomy
[{'content': 'Referred pain in external hemorrhoids is due to \nSelect and explain. \nA. Common pudendal nerve, B. Inferior rectal nerve, C. Splanchnic nerve, D. Sympathetic nerve', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Internal hemorrhoids are located on the inside lining of the rectum and cannot be felt unless they prolapse and push through the anus opening causing pain and itching. A thrombosed external hemorrhoid occurs when blood within the blood vessel clots, and may cause significant pain and swelling.', 'role': 'assistant'}]