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III. Reading Comprehension (30 points, 2 points for each item)
Passage One
Questions 21 to 25 are based on the following passage.
Can your cellular phone really give you cancer? The best answer science can offer so far is maybe.
Researchers have discovered that cellular--phone radiation(辐射) can cause subtle, short-term biological effects in humans-including changes in brainwave patterns during sleep—but their full significance remains to be determined. Given that uncertainty and the fact that everyone from the National Cancer Institute to the World Health Organization is investigating cellular—phone radiation, many experts caution that it is far too early to give the phones a clean bill of health.
Cellular phones work by transmitting radio waves to base stations that connect calls into a network. The waves are a form of non-ionizing(非离子的) radiation-unlike, say, X rays, which have the power to change the atoms in human cells to potentially hazardous ions. Non—ionizing radiation can also be dangerous. At the high levels found in radar or inside microwave ovens(微波炉), it can heat and severely damage human beings. The question for scientists is whether the low—energy (and low-heat) signals from cellular phones can do harm.
Cancer studies have been inconclusive since 1993,when a Florida man brought an unsuccessful charge that blamed his wife’s fatal brain tumor(肿瘤) on her use of a cellular phone. In a frequently quoted 1997 report, Australian researchers exposed mice to two daily 30-min. amount of cellular-phone radiation for up to 18 months. The mice developed tumors at twice the rate of animals that were radiation-free. But the results haven’t been widely quoted, and some scientists question their relevance. For now m the best advice science can offer about cellular phones is handle with care.
21. According to the passage, science cannot offer us a definite connection between ________.
[A] cellular-phone radiation and changes in brainwave patterns
[B] X rays and the atoms in human cells
[C] the use of cellular phones and cancer
[D] mice exposed to cellular-phone radiation and the development of tumors
22. “A clean bill of health” in the first paragraph means ________.
[A] the money paid for a treatment in a hospital
[B] a clean way of improving health
[C] the health that is improved through good habits
[D] a document of health stating the absence of disease
23. According to the passage, radio waves are different from X rays in that ________.
[A] the former are more dangerous
[B] the former are a form of non-ionizing radiation
[C] the latter are mainly used in hospitals
[D] the latter are low-energy and low-heat signals
24. The word “inconclusive” in the last paragraph means ________
[A] disapproved by the public
[B] not generally understood
[C] misleading people to a conclusion
[D] not leading to a definite result
25. According to the passage, it is advised that cell phones ________.
[A] be done away with
[B] be handled cautiously
[C] be researched scientifically
[D] be associated with cancer
参考答案：21. C?? 22. D?? 23. B?? 24. D?? 25. B
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