阅读下面的材料，然后根据材料内容回答问题。 What is to blame（归咎于） for the smog (雾霾) hitting China? The question that has bothered people for a long time got an answer recently. According to Wang Yuesi, a researcher at the Chinese Academy of Sciences (CAS), about 40 percent of PM2.5 pollutants in Beijing are the result of coal (煤炭) burning, from both local and outside the city. Surrounded by Hebei, a major area for coal burning, about 20 percent of Beijing’s pollutants come from outside the city. And we know there are many steel(钢铁) factories in Hebei, too. According to the CAS, each year Beijing burns 23 million tons of coal while Tianjin burns more than 70 million tons and Hebei a huge 270 million tons. “Coal burning is a primary source of sulfur oxide (SO2, 二氧化硫) which is the primary cause of PM2.5,” said Wang. The report of the CAS says that in the Jingjinji area (Beijing, Tianjin and Hebei), coal burning is responsible(负责任的) for 9 percent of primary particles (颗粒) that make up PM2.5. The coal burning also emits (排放) 69 percent of the total SO2 and 47 percent of nitrogen oxide (氮氧化物), which will greatly concentrate (加强浓度) the PM2.5 particles in the air. According to the air pollution plan, the Jingjinji area should reduce（减少） its PM2.5 concentration by 25 percent by 2017 from 2012 levels. To meet the standards, the report suggests great cuts in coal use in the area. “This is a very great goal but it is achievable with cooperation（合作） between cities instead of cities working on their own,” said Wang. 小题1:What’s the main cause of the smog hitting Beijing? ________________________________________________________ 小题2:Can we solve the problem with cooperation between cities ? ________________________________________________________ 小题3:Which is the primary cause of PM2.5? ________________________________________________________ 小题4:Why does Hebei produce a lot of PM2.5 pollutants? ________________________________________________________ 小题5:Who announced the result of the survey from CAS? ________________________________________________________