听力原文： We've become alarmed over the health center by the number of students who are experiencing hearing loss. First, I want to go over some basic about hearing. Then we can take a look at our school environment and see if we can figure out some ways to protect hearing. The leading cause of preventable hearing loss is excessive noise. Too much moderate noise for a long time or some types of intense noise for even a short time can damage hearing. Loudness is measured by decibels. One decibel is the lowest sound the average person can hear. Sounds up to 80 decibels generally aren't harmful. That's noise like traffic on a busy street. But anything louder than 80 decibels may hurt your hearing. Once you are up to 140 decibels, that's like a jet plane taking off, then you might even feel pain in your ears. Those are sure sign that your hearing's at risk. Even one exposure to a really loud noise at close range can cause hearing loss. So what you need to do is limit your exposure to harmful levels. If you pass along this handout, we can take a look at the decibel level of some common campus sounds. Notice how loud those horns are that people take to football games. They are really dangerous if blown right behind you. What is this passage talking about?