按要求完成下列句子。

1. My ruler is on the desk. (就画线部分提问)

    ____________________________ is your ruler?

2. His father is reading a book. (变成一般疑问句)

    _________ __________ ________ reading a book?

3. I can use a computer. (变成否定句)

    I ___________________________ use a computer.

4. Wu Yinfan is my good friend. (就画线部分提问)

    ____________________________ your good friend?

5. This is a chair. (变成复数)

    ____________________________.

一个圆柱体容器内放有一个长方形铁块．现打开水龙头往容器中灌水.3分钟时水面恰好没过长方体的顶面．再过18分钟水已灌满容器．已知容器的高为50厘米，长方体的高为20厘米，求长方体的底面面积和容器底面面积之比．