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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

admin2010-07-14  44
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.
Which of the following statements about the standard 90 db is NOT true?
选项 A、It suits everyone.
B、It can protect only 90 per cent of the working force.
C、It requires 16 quiet hours of rest each day for the ears to recover.
D、It can hardly be applied in reality.
答案A
解析 第二段说人们对噪音的接受能力因人而异，有人大约更敏感，有人则抗噪音能力强些，所以90分贝的标准不是理想的，不适用于任何人。因此选A。
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