Since January 2013, many cities in China have seen a lot of foggy days. In Beijing, only five days in January were free of smog (雾霾). What’s the difference between fog and smog? According to scientists, fog is made up of tiny (微小的) drops of water and also ice particles (颗粒) during very cold conditions. Smog is dirty air that looks like a mixture of smoke and fog, caused mainly by smoke from cars and factories in cities. An official for the Ministry of Environmental Protection told Beijing News that PM2.5 pollution is the main problem with air pollution. PM 2.5 refers to pollution with small particles 2.5 micrometers or less in diameter (直径). According to the Chinese Academy of Sciences, two main factors that cause PM 2.5 are motor vehicles and the burning of coal. Poor air has done harm to people’s health. Children and the elderly are more at risk.A.report from Beijing Children’s Hospital shows that from January 5 to January 11, 2013, half of the patients in the hospital came for respiratory (呼吸道的) problems. To respond to the air problem, the Chinese government and many Chinese people have started to take action. Beijing announced a plan to use clean fuel in government vehicles and plant trees. It asked citizens to set off fewer fireworks for the Spring Festival celebration. They suggested that cars with large emissions (排放) should be banned and factories should be closely watcheD. Three students from No. 4 High School in Beijing wrote a report to advise to fight the air pollution. “We hope more people will join us to protect our environment. With all our efforts, the blue skies will certainly return soon,” said Shi Yucong, 15, one of the three students. 1. The underlined phrase “were free of” means ____________. A. had some B. had many C. had no D. had more and more 2. According to the second paragraph, we can know ____________. A. smog is a mixture of fog and smoke B. smog is formed (形成) during cold hours C. fog is made up of drops of water with smoke D. smoke from cars and factories cause fog 3. Paragraphs 3 and 4 are mainly about ____________. A. what PM 2.5 is and what causes PM 2.5 B. how to prevent PM 2.5 pollution and how PM 2.5 looks C. what PM 2.5 is and how to protect ourselves against PM 2.5 D. how seriously PM 2.5 affects us and how to deal with PM 2.5 4. What is the best title for the passage? A.A.report about air pollution B. Let’s fight the air pollution C. Dirty air is bad for us D. The air in Beijing