请听下面一段独白,根据独白内容完成下列句子,每个空格不超过3个单词。将答案写在答题卡的相应位置。听独白前你将有50秒钟的时间阅读句子内容。独白读两遍。
16. Our earth is becoming worse and worse because of serious ______.
17. We need more land to deal with rubbish, so there won’t be enough ______ for people.
18. Next, we should keep ______ clean.
19. If we keep polluting it, it’1l be ______ for us to enjoy so much seafood in the future.
20. Everyone should play a part in ______.