必修2Unit 3　Computers课前10分钟概括大意    There are large sudden pollution increases during rush hours.Pollution levels fall during nighttime.The time of year also makes a big difference.Pollution levels tend to be at their lowest during spring and autumn when winds are freshest.Extreme cold or hot weather has a trapping effect and tends to cause a buildup of pollutants.此段落大意是：When pollution levels rise and fall?
漫画观赏 画面描述 　　A young man is running toward the end of a race，sweating all over.The end line ...