In today's world, almost everyone knows that air pollution and water pollution are harmful to people's health. However, not all people know that noise is also a kind of pollution, and this is harmful to people's health, too.    People who work and live under noisy conditions usually become deaf today. However, scientists believe that 10 percent of workers in Britain are being deafened by the noise where they work. Many of the workers who print newspapers and books, and who weave cloth become deaf. Quite a few people living near airports also become deaf. Recently it was discovered that many teenagers in America could hear no better than 65-year-old persons, for these young people like to listen to pop music and pop music is a kind of noise. Besides, noise produced by jet planes or machines will make people ill or even drive them mad.    It is said a continuous noise of over 85 decibels  can cause deafness. Now the government in many countries have made laws to control noise and make it less than 85 decibels.    In China, the government is trying to solve not only air and water pollution problems but also noise problems. Ten percent of the workers in Britain are being deafened because   _  .
they are working in noisy places they often listen to pop music they are busy in listening to other's talk they live near airports