This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
[{'content': 'Untoff phenomenon is \nSelect and explain. \nA. Worsening of symptom with cold, B. Relief of symptom with cold, C. Worsening of symptom with heat and exeion, D. Palsy of symptom with heat and excretion', 'role': 'user'}, {'content': "Answer: C \nExplanation: Harrison's principles of internal medicine 17th edition. *U/l visual blurring may occur following a hot shower or with physical exercise. Uhthoff's phenomenon (also known as Uhthoff's syndrome, Uhthoff's sign, and Uhthoff's symptom) is the worsening of neurologic symptoms in multiple sclerosis (MS) and other neurological, demyelinating conditions when the body gets overheated from hot weather, exercise, fever, or saunas and hot tubs. Ref Harrison20th edition pg 2345", 'role': 'assistant'}]