We know the sounds of cities are loud enough to cause great harm to people's hearing in the U.
S.One person out of twenty has got some hearing loss.And all over the world the situation is getting worse and worse all the time since the noise increases with the population.
With the development of machines,noise has also increased greatly in the 20th century.We live surrounded by loud planes,trucks and electric tools.TV sets and radios add up to 90 or J00 decibels,a certain unit used to measure the loudness of sound.A normal dialogue reaches 55 decibels; a plane goes to 100,and an ordinary train,reaching the station,can be twice as loud as the loudest plane.Disco music reaches about 118.At decibels the ear stops hearing sound,and pain starts.How terrible if things go on like this!
噪音污染
众所周知,在美国,城市巨大的噪音对人们的听力造成了极大的损害.每20个人中就有一个有不同程度的听力损伤.就世界范围看来,因为噪音随着人口的不断增长,而越来越严重,这种情况也愈发恶化.
20世纪,随着机械制造业的发展,噪音污染也日益加剧.我们生活在震耳欲聋的飞机、卡车和电器中.
电视和收音机加起来甚至达到90至100分贝(分贝：一种测定声音
大小的特定单位).人们普通的对话是55分贝；飞机飞行中为100分贝；而一列普通的火车在到站时音量能够达到最嘈杂的飞机的两倍；迪斯科音乐更是高达118分贝.到达分贝耳朵就会丧失听觉,感到痛苦.这样下去,该是一件多么可怕的事情啊!