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: Pediatrics
[{'content': 'The maximum risk of developing foetal varicella syndrome is when the exposure is between what period of pregnancy? \nSelect and explain. \nA. < 9 weeks, B. 13 -20 weeks, C. 20-24 weeks, D. 4 days before delivery', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 13-20 weeks is the critical period for foetal varicella syndrome.', 'role': 'assistant'}]