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  3. About two-thirds of the world’s population is expected to live in cities by

About two-thirds of the world’s population is expected to live in cities by

游客2024-11-25  11
问题     About two-thirds of the world’s population is expected to live in cities by the year 2020 and, according to the United Nations, approximately 3.7 billion people will inhabit urban areas some ten years later. As cities grow, so do the number of buildings that characterize them: office towers, factories, shopping malls and high-rise apartment buildings. These structures depend on artificial ventilation systems to keep clean and cool air flowing to the people inside. We know these systems by the term"air-conditioning".
    Although many of us may feel air-conditioners bring relief from hot, humid or polluted outside air, they pose many potential health hazards. Much research has looked at how the circulation of air inside a closed environment—such as an office building—can spread disease or expose occupants to harmful chemicals.
    One of the more widely publicised dangers is that of Legionnaire’s disease, which was first recognised in the 1970s. This was found to have affected people in buildings with air-conditioning systems in which warm air pumped out of the system’s cooling towers was somehow sucked back into the air intake, in most cases due to poor design. This warm air was, needless to say, the perfect environment for the rapid growth of disease-carrying bacteria originating from outside the building, where it existed in harmless quantities. The warm, bacteria-laden air was combined with cooled, conditioned air and was then circulated around various parts of the building. Studies showed that even people outside such buildings were at risk if they walked past air exhaust ducts.     Cases of Legionnaire’s disease are becoming fewer with newer system designs and modifications to older systems, but many older buildings, particularly in developing countries, require constant monitoring.
    The ways in which air-conditioners work to " clean" the air can inadvertently cause health problems, too. One such way is with the use of an electrostatic precipitator, which removes dust and smoke particles from the air. What precipitators also do, however, is to emit large quantities of positive air ions into the ventilation system. A growing number of studies show that overexposure to positive air ions can result in headaches, fatigue and feelings of irritation.
    Large air-conditioning systems add water to the air they circulate by means of humidifiers. In older systems, the water used for this process is kept in special reservoirs, the bottoms of which provide breeding grounds for bacteria and fungi which can find their way into the ventilation system. The risk to human health from this situation has been highlighted by the fact that the immune systems of approximately half of workers in air-conditioned office buildings have developed antibodies to fight off the organisms found at the bottom of system reservoirs. Chemical disinfectants, called " biocides", that are added to reservoirs to make them germ-free, are dangerous in their own right in sufficient quantities, as they often contain compounds such as pentachlorophenol, which is strongly linked to abdominal cancers.
    Finally, it should be pointed out that the artificial climatic environment created by air-conditioners can also adversely affect us. In a natural environment, whether indoor or outdoor, there are small variations in temperature and humidity. Indeed, the human body has long been accustomed to these normal changes. In an air-conditioned living or work environment, however, body temperatures remain well under 37℃, our normal temperature. This leads to a weakened immune system and thus greater susceptibility to diseases such as colds and flu. [br] Which of the following substance can NOT be found directly from an old ventilation system?
选项 A、Chemical disinfectants.
B、Bacteria.
C、Fungi.
D、Pentachlorophenol.
答案 D
解析 细节题。倒数第二段第二句指出，在旧式空调系统中，用于循环的水储存在特制的贮液器中，而贮液器的底部就是进入通风系统中的细菌和真菌的滋生地。第四句指出，为了达到无菌的目的要在贮液器中加入化学消毒剂，又称“杀菌剂”，当其剂量大到一定程度时也会变得危险，这是因为这类杀菌剂中往往含有五氯苯酚一类的化合物。后者与腹部癌症的发作有着极其密切的关系。因此细菌、真菌和化学消毒剂都是直接的致病因素，故排除[A]、[B]、[C]；“Pentachlorophenol”只是消毒剂成分中的一种物质，不是直接存在于空调系统中的，故答案为[D]。
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