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 colour of gingiva is due to \nSelect and explain. \nA. Capillaries, B. Thickness of epithelium, C. Thickness of keratinisation and pigmentation, D. All the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]