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: Surgery
[{'content': 'Most common cause of umbilicus does not separate at age of 2 years - \nSelect and explain. \nA. Raspbery tumour, B. Leukocyte adhesion deficiency, C. Patent urachus, D. Umblical granuloma', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]