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: Anatomy
[{'content': 'Neurulation is completed on day: \nSelect and explain. \nA. 14, B. 18, C. 21, D. None of the above', 'role': 'user'}, {'content': "Answer: D \nExplanation: Closure of the cranial neuropore occurs at approximately day 25 (18- to 20-somite stage), whereas the posterior neuropore closes at day 28 (25-somite stage). Neurulation is then complete, and the central nervous system is represented by a closed tubular structure with a narrow caudal poion, the spinal cord, and a much broader cephalic poion characterized by a number of dilations, the brain vesicles Ref: Langman's embryology 11th edition Chapter 5.", 'role': 'assistant'}]