B Smog(雾霾 ) is a big problem in many Chinese cities. But it seems that besides wearing a mask, few of us know what has caused the smog and what to do to beat it. Chai Jing, a former news hostess with China Central Television, discussed the questions in her documentary Under the Dome. The 103 - minute film was published on major Chinese video - sharing websites on Feb 28. In the film, Chai visits polluted places and talks to officials and scientists. She comes to the conclusion that burning too much coal and oil are the main causes of PM2.5 and smog. To make things worse, according to Chai, the coal and oil we are burning is of poor quality and don't meet the standards for environmental protection. Therefore, they have produced more harmful gas to pollute the air. To solve the problem, Chai suggests that we should clean our coal and oil or replace them with cleaner energy such as natural gas. In her film, Chai also pointed out that ordinary people can do something to help control smog too. For example, we live a greener life by using more public traffic. Or if we see things that could harm the environment, we can try to stop it. In one scene from the film , Chai sees a dirt mound in a building site exposed in the air, and asks the person in charge to cover it. When she sees a restaurant cooking without any suitable filter facilities, she calls the hotline 12369. The restaurant installed the filter a week later. Chen Jining, the new minister of environmental protection, praised Chai. "This film encourages ordinary people to care about the environment. This is what we need in the future. " 23.Which of the following is NOT Chai's suggestions towards reducing smog?