This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fertilization and Development of Embryo, Subject name: Anatomy
[{'content': 'Morula reaches uterus at? \nSelect and explain. \nA. 3 day after fertilisation, B. 4 day after fertilisation, C. 5 day after fertilisation, D. 6 days after fertilization', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. (b) 4 day after fertilisationRef: Langman's embryology 10/hed/p 38, Longman's medical embryology 12th ed/ 37-40", 'role': 'assistant'}]