根据对话内容，在空白处填写适当的话语（话语可能是一个句子，也可能是一个短语或一个词）。使对话完整。 (Dan and Kate are talking about pollution.) Dan: It is said that pollution is worse than before. Kate: Yes,  I have noticed this.  What do you think of pollution? Dan: It makes me a little worried. 1 ? Kate: Me too.  I think pollution is everyone's problem and it is everyone's duty to protect environment. Dan: Quite right! But as a teenager, 2 ? Kate: To start with, we should start a clean-up club. We can give out ads after school to tell people how important environment is. Dan: 3 !Besides this, we should make people know that pollution is the biggest challenge that they are facing. Kate: I agree with you.  If everyone can do something to keep our environment clean, our world will be 4 . Dan: Yes. As the saying goes. One finger cannot lift a small stone. Dan: What else? Kate: We shouldn't throw 5 everywhere, either. Dan: OK.  I'm sure we will be successful.