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': 'The mucous secretion differs from the secretion of serous as former has: \nSelect and explain. \nA. Little or no enzymatic activity., B. The ratio of carbohydrate to protein is greater., C. A larger amount of sialic acid., D. All of the above.', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The mucous secretion differs from secretion of serous in two important respects:\xa0\n\nThey have little or no enzymatic activity and probably\xa0serve mainly for lubrication and protection of the oral tissues\nThe ratio of carbohydrate to protein is greater and\xa0larger amounts of sialic acid acid and occasionally sulfated\xa0sugars are present.', 'role': 'assistant'}]