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Passage Eleven (The Affect of Electricity on Cancer) Can electricity cause cancer? In a society that literally1 runs on electric power, the very idea seems preposterous2. But for more than a decade, a growing band of scientists and journalists has pointed3 to studies that seem to link exposure to electromagnetic fields with increased risk of leukemia and other malignancies. The implications are unsettling, to say the least, since everyone comes into contact with such fields, which are generated by everything electrical, from power lines and antennas4 to personal computers and micro-wave ovens. Because evidence on the subject is inconclusive and often contradictory5, it has been hard to decide whether concern about the health effects of electricity is legitimate-or the worst kind of paranoia6. Now the alarmists have gained some qualified7 support from the U.S. Environmental Protection Agency. In the executive summary of a new scientific review, released in draft form late last week, the EPA has put forward what amounts to the most serious government warning to date. The agency tentatively concludes that scientific evidence “suggests a casual link” between extremely low-frequency electromagnetic fields-those having very longwave-lengths-and leukemia, lymphoma and brain cancer, While the report falls short of classifying ELF fields as probable carcinogens, it does identify the common 60-hertz magnetic field as “a possible, but not proven, cause of cancer in humans.” The report is no reason to panic-or even to lost sleep. If there is a cancer risk, it is a small one. The evidence is still so controversial that the draft stirred a great deal of debate within the Bush Administration, and the EPA released it over strong objections from the Pentagon and the Whit8 House. But now no one can deny that the issue must be taken seriously and that much more research is needed. At the heart of the debate is a simple and well-understood physical phenomenon: When an electric current passes through a wire, tit generates an electromagnetic field that exerts forces on surrounding objects, For many years, scientists dismissed any suggestion that such forces might be harmful, primarily because they are so extraordinarily9 weak. The ELF magnetic field generated by a video terminal measures only a few milligauss, or about one-hundredth the strength of the earth’s own magnetic field, The electric fields surrounding a power line can be as high as 10 kilovolts per meter, but the corresponding field induced in human cells will be only about 1 millivolt per meter. This is far less than the electric fields that the cells themselves generate. How could such minuscule10 forces pose a health danger? The consensus11 used to be that they could not, and for decades scientists concentrated on more powerful kinds of radiation, like X-rays, that pack sufficient wallop to knock electrons out of the molecules12 that make up the human body. Such “ionizing” radiations have been clearly linked to increased cancer risks and there are regulations to control emissions13. But epidemiological studies, which find statistical14 associations between sets of data, do not prove cause and effect. Though there is a body of laboratory work showing that exposure to ELF fields can have biological effects on animal tissues, a mechanism15 by which those effects could lead to cancerous growths has never been found. The Pentagon is for from persuaded. In a blistering16 33-page critique of the EPA report, Air Force scientists charge its authors with having “biased the entire document” toward proving a link. “Our reviewers are convinced that there is no suggestion that (electromagnetic fields) present in the environment induce or promote cancer,” the Air Force concludes. “It is astonishing that the EPA would lend its imprimatur on this report.” Then Pentagon’s concern is understandable. There is hardly a unit of the modern military that does not depend on the heavy use of some kind of electronic equipment, from huge ground-based radar17 towers to the defense18 systems built into every warship19 and plane. 1. The main idea of this passage is [A]. studies on the cause of cancer [B]. controversial view-points in the cause of cancer [C]. the relationship between electricity and cancer. [D]. different ideas about the effect of electricity on caner20. 2. The view-point of the EPA is [A]. there is casual link between electricity and cancer. [B]. electricity really affects cancer. [C]. controversial. [D].low frequency electromagnetic field is a possible cause of cancer 3. Why did the Pentagon and Whit House object to the release of the report? Because [A]. it may stir a great deal of debate among the Bush Administration. [B]. every unit of the modern military has depended on the heavy use of some kind of electronic equipment. [C]. the Pentagon’s concern was understandable. [D]. they had different arguments. 4. It can be inferred from physical phenomenon [A]. the force of the electromagnetic field is too weak to be harmful. [B]. the force of the electromagnetic field is weaker than the electric field that the cells generate. [C]. electromagnetic field may affect health. [D]. only more powerful radiation can knock electron out of human body. 5. What do you think ordinary citizens may do after reading the different arguments? [A].They are indifferent. [B]. They are worried very much. [C]. The may exercise prudent21 avoidance. [C]. They are shocked. 点击  收听单词发音
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