17. Many rivers and lakes have become __________ in our countries. (pllute)

答案:polluted　 get／become+过去分词表示状态的改变，所跟过去分词或形容词作表语。

16. Manatees usually __________ about 1 000 pounds. (weight)

答案:weigh　 weight，名词“重量”，weigh 作及物动词时是“称，量”之意，作不及物动词时为“重……，称……重量”。

15. This kind of animals are very _________. Don’t get close to them. (aggressive)

答案:aggressive

14. The man _________ patted the boy on the shoulder. (gentle)

答案:gently

13. Don’t use paper towels and napkins. It’s bad for the enviroment.　　 　　_____________

答案:and→or

12. It’s hard to stop to ride in cars.　　　　　　　　　　　　　　　　　　 _____________

答案:to ride→riding　 stop doing sth.表示停下正在做的事情，stop to do sth.表示停下去做另一件事。

11. This kind of bowl is made from bamboo.　　　　　　　　　　　　　 　_____________

答案:from→of　 be made from 由……制作，表示成品中看不出原材料。

10. Saving endangered animals are very important to us.　　　　　　　　　 _____________

答案:are→is　 非谓语动词作主语时，谓语动词用单数。

9. He is doing his homework as more careful as he can.　　　　　　　　　　 _____________

答案:去掉 more　 as…as 原级比较，只接形容词或副词的原级。

8. S_________ is another way of saying “waste things”.

答案:stuff