根据短文内容，选择最佳答案。

Schedule a Tour

    University of South Carolina （USC) is famous for its warm southern hospitality（好客）. Schedule a visit and feel it in person. Our walking tours are led by current students, called University Ambassadors, who are looking forward to telling you what it's like to live and study in USC. Our walking tours run Monday through Friday and most are around 2 hours. The university will be closed on Tuesday, July 4, 2017 in observance of the holiday. We welcome your visit year round and will be ready for you, rain or shine. Please refer to the list below to determine which tour is best for you and remember to book at least two weeks in advance.

一个半径为5cm的量角器。它的周长是多少？

3.14×5×2÷2＝15.7(cm)

答：它的周长是15.7cm。

当今世界，美国是唯一的超级大国，俄罗斯拥有庞大的军事力量，日本拥有强大的经济力量，中国是世界上最大的发展中国家，这反映出 （   ）