【正确答案】 B

【答案解析】分析：estimate的用法比较单一； 1．be estimated to be/have/cost etc The tree is estimated to be at least 700 years old. 2．estimate something at something Organizers estimated the crowd at 50,000. 3．estimate that Scientists estimate that smoking reduces life expectancy by around 12 years on average. 4．estimate how many/what etc It is not easy to estimate how many people have the disease. 参考译文：据估计，宇宙的年龄大约是100亿到200亿年。