用所给词的适当形式填空。

1. Ms Ba sometimes watches her students having fun _____ (play) on the playground.

2. Go _____ (cross) the bridge, you can see a tall tree with many flowers on it .

3. Children often enjoy _____ (they) at school .

4. Sheep like to eat grass and _____ (leaf).

5. Please _____ (be) quiet when you are with pandas in the zoo.

6. We sometimes listen to some _____ (relax) music when we're tired.

7. Hunan Street is a good place _____ (have) fun..

8. I like elephants because they are so _____ (beauty).

9. Are _____ (thief) afraid of the police? Yes, very much.

10. Do you think koalas are very _____ (friend) to people?

原水（未经过处理的水）中含有泥沙、悬浮物和细菌等杂质。在水中撒些明矾，可除去水中的泥沙、悬浮物，使水变澄清；可用次氯酸（HClO）杀死细菌。氯气溶于水时可生成盐酸和次氯酸。某水厂生产自来水的步骤如下：

（1）可以除去水中的泥沙和悬浮物杂质的步骤为________（填编号）。

（2）能消毒杀菌的步骤为________。