This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Development period- week 1,2,3,4, Subject name: Anatomy
[{'content': 'Morula has how many cells \nSelect and explain. \nA. 8, B. 16, C. 32, D. 64', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Morula is a 16 cell stage Advanced morula >32 cell stage Advanced morula enters uterine cavity on day 4 Blastocyst is formed by end of day 4 covered with zona pellucida', 'role': 'assistant'}]