用所给动词的适当形式填空。

1.What's the _____ (mean) of "Olympics"?

2.The farmers don't use cows _____ (do)  work anymore.

3.The teacher told the students to take_____ (clean) the classroom.

4. He kept_____ (think) about the math problem.

5. We should practice _____(read) English  every morning.

水是生命活动的重要物质．下列有关水的变化，属于化学变化的是（　　）

A．水蒸发

B．水结冰

C．水沸腾

D．水分解