若sinα=2cosα，则$\frac{\sin \kappa -\cos \alpha }{\sin \alpha +\cos \alpha }$的值为（　　）

Dear Kelly,

    Today is Friday. It's evening in Shanghai. I'm writing to tell you something about my life (生活).My mother is cooking. My father is watching sports news(新闻).My brother, Tim, is playing computer games. My little sister, Mary, is drawing. My dog Dick is taking my hat to me. He wants me to put it on and go out for a walk with him. He's a clever dog and he is often excited(兴奋的)to see me.

    Outside, I can hear cars and buses coming and going. Also there are some boys playing ball games. It's a noisy(吵闹的)but happy evening. Do you think so?

    What are your family doing now?

    Please write me soon.

Yours,

Daniel

根据材料内容选择最佳答案。