已知正数$x,y$满足$x+2y=1$，则$\frac{1}{x}+\frac{1}{y}$的最小值为（   ）

阅读理解

     Many teenagers feel that the most important people in their lives are their friends．They believe that their families don't know them as well as their friends do．In large families，it is quite often for brothers and sisters to fight each other and then they can only go to their friends for some ideas．It is very important for teenagers to have one good friend or a group of friends．

     Even when they are not with their friends，they usually spend a lot of time talking with each other on the phone．This communication is very important in children's growing up，because friends can discuss something．These things are difficult to say to their family members．

    However，parents often try to choose their children's friends for them．Some parents may even stop their children from meeting their good friends．Have you ever thought of the following questions?

    Who choose your friends? Do you choose your friends or your friends choose you? Have you got a good friend your parents don't like? Your answers are welcome．

如图，北京奥运会的场馆鸟巢、水立方等设计精巧，已经成为建筑史上的杰作。而大约7000年前的我国原始人类建造的房屋也令人惊叹，看下图房屋结构，结合地理环境因素，说出它是哪一远古居民的房子（    ）