Scientists now tend to agree that the noise level for potential hearing loss begins at about 7 decibels. Some of them are very concerned because normal daily life often exposes people to nois levels of about 70 decibels even inside their homes. Cities have always been noisy, but noise is nm spreading to areas that were quiet just a few years ago. Clearly, something must be done or noise will seriously and permanently maim the populatior Fortunately, the knowledge and methods to control noise already exist. As a matter of fact, this i one instance where the knowledge of control methods exceeds the knowledge about the effects o human life and on the environment. There are two common means for control. The first is reducing noise at its source, and th second is changing the sound path by distance or by shielding. The second approach is being used more often today as people become more aware of th danger of noise. New building codes require better sound insulation in homes and apartments. Mor and more towns are passing zoning ordinances that try to segregate noisy factories or airports fro~ residential areas. Sound-absorbent materials and construction designed to block sound paths ar slowly coming into use in offices and homes. New highways are being built to redirect traffic nois up and away from nearby areas. Aircraft are increasingly being required to use reduced powe flights around airports. There are many examples of available noise control methods that are not being used. Mor flexible building codes would permit the use of quieter kinds of plumbing pipes. Sound-absorbint materials can reduce the noise of motors and engines. Power generators can be quieted with baffles exhaust silencers, and sound absorbers. Truck tires can be made with quieter treads. In many cases the cost of building quieter machines is the same or only slightly higher than that of the current noisy ones. Even though the new equipment may cost more initially, it can prove more profitable in the long run. The new jumbo jets, for example, are quieter than the older ones, yet they are more powerful and carry twice as many passengers. All of these methods are only partial measures as noisy levels continue to rise. Most specialists in the field agree that much of the solution must come from eliminating some of the noise at its source, therefore saving through prevention the large costs of hearing loss.
单选题
The noise level for possible hearing loss begins at about______ A. 30 decibels B. 75 decibels C. 100 decibels D. none of the above
【正确答案】
D
【答案解析】[解析] 原文第一段第一句明确指出“the noise level for potential hearing loss begins at about 70 decibels”。因此A、B、C三个选项均不正确。
单选题
Jet pilots are being advised to land ______ A. on longer runways B. from nearby areas C. after dark D. with reduced power
【正确答案】
D
【答案解析】[解析] 根据第四段最后一句“Aircraft are increasingly being required to use reduced power flights around airports”可知，D选项正确，其他选项未被提及。
单选题
How many practical means for controlling noise does the author present? A. One. B. Two. C. Three. D. Four.
【正确答案】
B
【答案解析】[解析] 本文在第三段明确指出“There are two common means for control”，并一加以 介绍，因此本题答案为B项。
单选题
The reader can assume that airport of the future will______ A. have runways in a north-south pattern B. be located in unpopulated areas C. be required to warn passengers of high noise levels D. in nearby areas
【正确答案】
B
【答案解析】[解析] 根据第四段第三句“More and more towns are passing zoning ordinances that try to segregate noisy factories or airports from residential areas”可知，现在越来越多的城镇通过分区 条例，计划将噪声污染严重的工厂和机场与居民区分开。那么未来机场可能会建在离居民区 远的地方，即无人居住的地区。因此正确答案是B。
单选题
Jumbo jets are mentioned as examples of______ A. efficient transportation with low levels of noise B. vehicles that cause serious air pollution C. scientific advances that do more harm than good D. quieter and older vehicle
【正确答案】
A
【答案解析】[解析] 根据第五段最后一句“The newjumbojets…they are more powerful and carry twice as many passengers”可知，新式的大型喷气式飞机能量更高，并且能够装载更多的 旅客。这说明，新式飞机噪声污染低而运输效率高。因此A项正确。其他选项不是拿喷 气式飞机举例的目的。