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: Physiology
[{'content': 'Not a feature of REM sleep: \nSelect and explain. \nA. Bruxism, B. Irregular breathing, C. Muscle tone in the body is depressed, D. Is associated with active dreaming', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Bruxism REF: GUYTON & HALL, Ganong, various internet resources. See APPENDIX-11 for "SLEEP PHYSIOLOGY"', 'role': 'assistant'}]