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': 'Rate of primary dentin formation is \nSelect and explain. \nA. 4μm/day, B. 5μm/day, C. 6μm/day, D. 7μm/day', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Secondary dentin forms at a slower rate (1μm/day) than primary dentin (4μm/day) and regularly but not uniformly—more formation is seen on the roof and floor of the pulp chamber. Hence this dentin is also known as regular secondary dentin. If the dentin forms as a reaction to an irritant (trauma or dental caries) to protect the pulp, it is called reparative/reactive/tertiary/irregular dentin', 'role': 'assistant'}]