补全对话。（共4小题，每小题1分；计4分）
Li Yang: Good morning. Mathew.
Mathew: Good morning, Li Yang. 小题1:
Li Yang: There's still smog (雾霾) today. We'll have to go to school with face masks(口罩).
Mathew: 小题2: According to the news, PM2.5 pollution is the main problem with air pollution.
Li Yang: Yes, and air pollution has done harm to people's health.
Mathew: So the Chinese government and Chinese people must take action to fight it.
Li Yang: 小题3:
Mathew: Yeah. Since PM2.5 is mainly caused by vehicles(机动车)and factories, cars with large
emissions(排放)should not be allowed and factories should be closely watched.
Li Yang: I agree. 小题4: And we suggest making the blue skies return for good.
Mathew: I hope so, too.
