自行车是同学们常用的交通工具，请把对应题号填在横线上．

①通过增大压力来增大摩擦的是 ____ ；

②通过增大接触面的粗糙程度来增大摩擦的是 ____ ；

③通过加润滑油来减小摩擦的是 ____ ；

④通过用滚动代替滑动来减小摩擦的是 ____ ；

A．脚蹬子表面做的粗糙不平；

B．刹车时要用力捏闸

C．车轮做成圆形的；

D．要经常给链条上油．

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。

水是生产生活中不可缺少的物质，下列关于水的说法中正确的是（   ）