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': 'Limb buds appear at week: \nSelect and explain. \nA. 6, B. 5, C. 3, D. 4', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Upper limb buds appear by the end of week 4 and about 2 days later lower limb buds appear (beginning of week 5).', 'role': 'assistant'}]