我常常梦想:被清脆的鸟鸣声唤醒,被明媚的阳光照耀,被参天的大树遮蔽,被孩子们欢快的声音包围。但随着社会的发展,虽然科技让我们的生活更加舒适、方便,也同时给我们增添了许多烦恼。例如汽车的问世和发展,极大地方便了人类的活动,有人说它无异是缩小了地球,延长了人的生命。不过汽车在造福人类的同时,也带来了危害,而且这种危害日益严重,因此有人称它为“城市杀手”。汽车排出的尾气严重威胁人类健康和城市环境,如今世界上许 I often dreamed of being awakened by the crisp sound of the birdsong, shining brightly by the sunshine, shaded by the towering trees and surrounded by the cheerful voices of the children. However, with the development of society, although technology has made our life more comfortable and convenient, it has also added a lot of troubles to us. For example, the advent and development of automobiles have greatly facilitated human activities. Some people say that it is the same as narrowing the earth and extending human life. However, the car at the same time for the benefit of mankind, but also brought harm, and the growing harm, so some people call it “city killer.” Exhaust emissions from cars pose a serious threat to human health and urban environment, and the world is now promised