调试超声波检测仪时，测得t0=5μs，已知某测点声距L=40cm，仪器显示声时为10

What do former American president Bill Clinton and rock musician Pete Townshend have in common.'? Both men have hearing damage from exposure(暴露，接触) to loud music, and both now wear hearing aids（助听器） as a result. As a teenager, Clinton played saxophone in a band. Townshend, who has the more severe hearing loss, was a guitarist for a band called the Who. He is one of the first rock musicians to call the public's attention to the problem of hearing loss from exposure to loud music.
Temporary（暂时） hearing loss can happen after only 15 minutes of listening to loud music. One early warning sign is when your ears begin to feel warm while you listen to music at a rock concert or through headphones. One later is that an unusual sound or a ringing is sometimes produced in your head after the concert.
"What happens is that the hair cells in the inner ear are damaged, but they're not dead," says physician and ear specialist Dr. Sam Levine. According to Dr. Levine, if you avoid further exposure to loud noise, it's possible to recondition the cells（细胞） somewhat. However, he adds, "Eventually, over a long period of time, hair cells are permanently damaged." And this is no small problem.
What sound level is dangerous? According to Dr. Levine, regular exposure to noise above 85 decibels (分贝) is considered dangerous. The chart below offers a comparison of decibel levels to certain sounds. Here's another measurement you can use. If you're at a rock concert and the music is so loud that you have to shout to make yourself heard, you' re at risk for hearing loss. That's when wearing protective devices such as earplugs becomes critical.
The facts are pretty frightening. But are rock bands turning down the volume.'? Most aren't. "Rock music is supposed to be loud," says drummer Andrew Sather."I wouldn't have it any other way. And neither would the real fans of rock. "
Continued exposure to loud music and the failure to wear earplugs can lead to deafness, according to Dr. Levine. He states, "There's no cure for hearing loss. Your ears are trying to tell you something. That ringing is the scream of your hair cells dying. Each time that happens, more and more damage is done. "

Levels of Common Noises Normal conversation                            50 — 65 dB Food blender                                  88 dB Jet plane flying above a person standing outside      103 dB Rock band during a concert                      110 — 140 dB

小题1:From Paragraph 1, we can learn that ___________                  .

A．loud music is a major cause of hearing loss

B．famous people may have hearing problems

C．teenagers should stay away from school bands

D．the problem of hearing damage is widely known

小题2:In Paragraph 3, the underlined word "recondition" means__________ .

A．not to be seen	B．to fill with sound
C．to become larger in size	D．to make good again

小题3:The purpose of the chart at the end of the article is to show__________   .

A．a list of harmful sounds

B．the effect of rock concerts

C．the noise levels of sounds

D．relationship between daily activities and hearing loss

小题4:Which of the following statements will Dr. Sam Levine probably agree?

A．When your ears feel warm, your hair cells are dead.

B．Drummer Andrew Sather gives good advice.

C．Many are at the risk of losing hearing.

D．Doctors know how to deal with hearing loss.