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  3. Noise enters our ears as powerful waves of mechanical energy. Scientists measure sound intensity in decibels (db), with each dou

Noise enters our ears as powerful waves of mechanical energy. Scientists measure sound intensity in decibels (db), with each dou

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问题     Noise enters our ears as powerful waves of mechanical energy. Scientists measure sound intensity in decibels (db), with each doubling of energy adding ten decibels. Ordinary conversation measures about 60 db; a child’s scream hits around 90 db. On this logarithmic scale, the scream is potentially 1,000 times more powerful.
    Each day, over five million Americans are exposed on the job to at least 90 db, the maximum safe level for an eight-hour period according to the federal Occupational Safety and Health Administration. "This standard isn’t ideal, because noise affects individuals differently," says William Clark of Washington University’s Central Institute for the Deaf in St. Louis.  "In theory, the standard should protect the lifetime hearing ofg0 percent of workers. However, it assumes that a worker’s ears will have 16 hours of quiet each day during which to recover -- an unlikely assumption for most people."
    Sound causes thousands of tiny hairs in the inner ear to vibrate. These vibrations trigger nerve impulses to the brain, which are perceived as sound. Prolonged exposure to 85 db or more, or far shorter exposure to very intense levels -- such as the 140-db shock waves from a shotgun blast -- can irrevocably damage some of these delicate inner-ear hairs. Ronald Reagan suffered permanent injury during his acting days when a 38-caliber pistol loaded with blanks was fired near his right ear. As a result, he now wears a hearing aid. Audiologists predict that by the year 2000, as many people could be wearing hearing aids as now wear contact lenses.
    Many people believe that weaker hearing is an inevitable part of aging. But studies show that those who live in low-noise environments tend to have very little hearing loss in old age.
    In noisy industrial nations, however, even young people suffer damaged hearing. David Lipscomb, a former professor of audiology at the University of Tennessee at Knoxville, tested over a thousand incoming freshmen and discovered that six of every ten had heating loss typical of the elderly. Rock music is one cause. The noise in a reek-concert hall can easily exceed 120 db, roughly the level of an air-raid siren. High-tech gadgets such as powerful portable stereos also threaten to put our hearing into a downward spiral.
Why does Ronald Reagan have to suffer permanent injury of heating? Because _______.
选项 A、his tight ear has been damaged
B、his nerve system is inefficient
C、there is some problem with his brain
D、some of the delicate hairs in his inner ear have suffered a great damage
答案D
解析 第三段说里根做演员的时候有人以一支38毫米口径的枪在他右耳附近开了枪，他的听力因此受损。听力受损时其实是内耳里细微的小茸毛受了伤害，而不是脑子或神经的问题。也可能这方面的损伤对听力也有影响，但这不在本篇的范围内，本篇也未提，因此答案为D。
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