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: Dental
[{'content': 'A cold test best localizes \nSelect and explain. \nA. Pain of pulpal   origin., B. Periodontal pain., C. Pulp necrosis., D. Referred pain.', 'role': 'user'}, {'content': "Answer: A \nExplanation: Hyperalgesia\xa0 is\xa0 manifested\xa0 in endodontic pain patients when noxious stimuli (e.g., refrigerant\xa0 sprays\xa0 or\xa0 carbon\xa0 dioxide\xa0 snow\xa0 used\xa0 in\xa0 the\xa0 cold\xa0 test) produce much more pain than they would in teeth with normal pulp tissues. Spontaneous pain involves episodes of pain that seem to\xa0 be\xa0 unprovoked.\xa0 All these changes can be partly Explained by sensitization of peripheral nerve endings in the pulp.\nCohen's Pathway of the Pulp ed:11th Pg551", 'role': 'assistant'}]