在△ABC中，a，b，c分别是角A，B，C的对边，设a+c=2b，则tan$\frac{A}{2}$•tan$\frac{c}{2}$的值为（参考公式：sinA+sinC=2sin$\frac{A+C}{2}$cos$\frac{A-C}{2}$）（　　）

    Bryant is my uncle. I know a lot ____(关于) him. He has a ____(儿子). He reads a lot in the city ____(图书馆). My uncle can ____(拼写) many English words. He is very ____(井井有条的). He ____(总是) puts his books in the bookshelf. I ____(必须) learn from him.He also likes animals. He has____(一些)pet ducks and two pet dogs. One dog is called ____(零) and the other is called One. My uncle is ____(他们的) good friend.