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': 'Gingivitis is initiated most frequently by: \nSelect and explain. \nA. Pregnancy, B. Malocclusion, C. Vitamin deficiency, D. Local irritating factors', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]