This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'What is the risk of downs syndrome in a 35-year-old pregnant woman? \nSelect and explain. \nA. 1 in 75, B. 1 in 100, C. 1 in 250, D. 1 in 1000', 'role': 'user'}, {'content': "Answer: C \nExplanation: Age of the motherRisk of Down&;s syndrome351 in 250361 in 192371 in 149381 in 115391 in 89401 in 69Reference: William's obstetrics; 25th edition; Chapter 14; Prenatal Diagnosis", 'role': 'assistant'}]