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': "Perikymata are the external surface manifestations of \nSelect and explain. \nA. Enamel rods, B. Incremental lines of retzius, C. Nasmyth's membrane, D. Pellicle", 'role': 'user'}, {'content': 'Answer: B \nExplanation: The number of perikymata gradually decreases form cervical region to occlusal or incisal region because of undisturbed development of enamel prior to birth. Perikymata are usually absent in prenatally developed occlusal parts of deciduous teeth, whereas they are present in postnatal cervical parts.', 'role': 'assistant'}]