Parties, iPods, concerts, movies, TV shows, video games, traffic. All of these things of the modern world make life entertaining and enjoyable. But our 21st-century lifestyle is also loud and, if we don't take notice, it can have an effect on our hearing. Most teenagers don't think about hearing loss. But if you experience any of the followingsymptoms , you may already be hearing damaged: you make efforts to hear normal talk, you have to turn up the TV or radio so high that others complain, you watch other people's expressions to understand what they are saying, you ask people to repeat themselves, you misunderstand what people are saying or you hear ringing in your ears. iPods and other MP3 players are as common as the clothes you wear, and just as fashionable. But if you turn up an iPod to more than 60 percent of itsmaximum volume , and listen to music for more than an hour, you are asking for trouble. And, it does not matter if the music you play is classical, rock or heavy metal. Some researchers find that young people who break the so-called 60-percent/60-minute rule in listening to iPods are at the risk of suffering hearing loss. Why is an iPod dangerous? With ear buds placed directly in the ear canal and high-volume music played over a long period of time, it's like working in a loud factory all day, being amaintenance person under a jet airplane or using ajackhammer on a building site. Similarly, iPod music can cause a short time orpermanent hearing damage. A loud iPod can cause aruptured eardrum and, over time, may cause permanent damage to the tiny hairs in the inner ear. If these tiny hairs are damaged, they cannot effectively send sounds to theauditory nerves that connect to the brain. If this happens, hearing loss becomes permanent. This passage is mainly about  _  .
music that teenagers like hearing problems caused by the loud world ways that teenagers enjoy music dangerous modern lifestyles of teenagers.