水体污染是指大量的污染物排入水体，水体及周围的生态平衡遭到破坏．水体污染的主要来源有工业污染、______、______．自然界的水所处环境不同，往往含有不同的杂质，欲使其转化为纯净水，需要运用适当的净水方法，以下是一些常用的净水方法，请选取合适的序号填空．

①利用活性炭吸附；②利用静置或加絮凝剂的方法进行沉淀；③过滤；④蒸馏上述方法中，只能除去不溶性杂质的是______，只能能除去有机色素或异味的是______，能除去大多数杂质，并使硬水软化的是______，上述方法按净化程度由低到高排列的顺序是______．

用动词的适当形式填空。

1. Chinese people _________ never _________(forget) the earthquake in Tangshan in1976.

2. Would you please ________(not prevent) me from becoming a member of the Birdwatching Club?

3. I've got no idea about how _________(stay) alive in the wild.

4. Luke spent as little time as he could __________(play) computer games.

5. My father encourages me _________(not lose) hope any time.

6. Jack said he ___________ (mop) the water up at that time.

7. Did you have a nice time ______(ski) last week?

8. I hope you _____ (not make) the same mistake again.

9. Look, Daniel __________ (have) an application form in his hand.

10. Laura __________(learn) another language next year, isn't she?