Environmental problems are becoming more and more serious all over the world. For example, cars have made the air unhealthy for people to breathe and poisonous gas is given off by factories. Trees on the hills have been cut down and waste water is being poured continuously into rivers.Furthermore, wherever we go today, we can find rubbish carelessly disposed. Pollution is, in fact, threatening our existence.    The earth is our home and we have the duty to take care of it for ourselves and for our later generations. Fortunately, more and more people have realized these problems.