l3. 小犀牛会得这种病是因为生它的母犀牛太老了，老犀牛 体内有toxic chemical elements，会导致疾病，只要让年轻的犀牛生育就可以了。
Independent writing task
Some companies provide important products or service, but also damage environment. Some people believe that government should require more penalty, higher tax and larger fine of these companies, while others believe there are better ways. Which do you prefer?
there are better ways
Moreover, shutting down the factories that produced air pollution is another more effective way to reduce the toxics in the environment. In fact, most of the air pollution comes from the disqualified factories, not from the wasted gases from the cars. After the city government of Beijing shut down hundreds of factories around the city in 2008, the air quality of Beijing increased by 40%. The blue sky above the skyscrapers appeared for more than a month, a sight that has never been seen for the past ten years. In such case, regulating the factories that produced air pollution effectively improved the quality of air.