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.