已知等差数列{a_n}中，$a_2=6,a_5=15$，若$b_n=a_{2n}$，则数列$\left\{b_n\right\}$的前5项和等于（   ）

阅读下面短文，并借助上下文和插图补充所缺信息。每个空格只能填写一个单词。

    Li Na is ____ Chinese professional(职业的) tennis player. Li has won 5WTAs and 19 ITF singles titles. Li Na was born ____ February 26, 1982 in Wuhan, China. When Li was 6 years old, she became a badminton ____, but her coach kept noticing that she looked as if she were playing tennis. By the time she was 8, her coach ____ her parents if she could switch to tennis, which she did at the ____ of 9. In 1997 Li ____ China's National Tennis Team andturned professional in1999. At the end of 2002, Li Na ____ the national tennis team to study at Huazhong University of Science and Technology, where she completed her bachelor(本科) degree in journalism. However, Li returned to the national team in 2004, Jiang Shan ____ Li and became her personal coach in 2006. In 2008 Li finally left the national team, becoming a free player. Li ____ English very well. She has a great sense of humor, too. She can move fast in her tennis playing. So she can ____ many other players and get many honors in her career (生涯). She is the most successful tennis player in China.

我国已启动“单独二孩”政策，即夫妻双方一人为独生子女，第一胎非多胞胎，即可生二胎。据此完成下列各题。