什么是发电机的同期操作？同期操作有哪两种？

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什么是发电机的同期操作？同期操作有哪两种？

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8[阅读题] Just as exercise strengthens the heart and lungs, bones and muscles, it may also power up the brain. A succession of scientific studies of animals implies that physical activity has a positive effect on mental functioning. “It’s clear that the brain benefits from exercise,” says brain scientist William Greenough of the University of Illinois at Urbana-Champaign. His studies with rats have demonstrated two primary effects of activity: vigorous physical exercise provides the brain with more fuel, and skill-based exercise increases the formation of connections in the brain, which, according to the proposals of some scientists, may make the brain better able to process information. In one experiment, laboratory rats were separated into three groups. One group was exercised by running inside an automatic wheel, a second group improved their skills in a complicated obstacle course, and a third group was inactive. “The animals that learned to go through the obstacle course exhibited a greater number of brain connections than the animals in the exercised or inactive groups,” Greenough said. “In contrast, the animals that exercised inside the automatic wheel possessed a greater density of blood vessels in the brain than did either of the other two groups of animals.” Learning a new dance step may boost the brain in the same way that learning a language can, he says. And if the dance is a good physical exercise as well, the benefits multiply. Young brains may be especially able to boost brain power through exercise, suggested another of Greenough’s experiments that showed the most significant changes in the brain occurred among rats that had been exercised when very young. And while animals aren’t people, he says it is logical to make the inference that an effect found in rats may also apply to humans. Human studies have focused primarily on older adults and suggest that regular exercises can improve the speed with which the brain processes information. Measurements made by Arthur Kramer at the University of Illinois demonstrated that inactive adults, aged 63 to 82, could hit buttons faster in response to a tone after they went through a 10-week water exercise course. A corresponding control group that didn’t exercise showed no improvement. This boost in reaction time after exercise training may occur because declines associated with getting old could actually stem from declines in physical condition. Some scientists speculate the reduction in mental function often attributed to getting old may really be a penalty of neglecting to stay physically active, in addition to related factors such as medicines and poor diet. “In older people, an exercise program appears important for brain maintenance,” says Daniel M. Landers, professor of exercise science at Arizona State University, who recently published an article reviewing the scientific literature on activity’s effect on the brain. Numerous studies show that children who engage in regular physical activity do better in school than their inactive classmates. But until recently, the academic edge gained by participating in sports was thought to come from the increased self-confidence, the better mood, and the ability to concentrate that comes from burning off steam in exercise. Now, however, some scientists have revised their way of thinking, and point to possible physical connections. 1. What makes the brain better able to process information? A) Vigorous physical exercise. B) Skill-based exercise. C) Both of them. D) Neither of them. 2. While _______ of rats showed a greater number of brain connections, _______ had a greater density of blood vessels in the brain. A) the first group / the third group B) the second group / the third group C) the first group / the second group D) the second group / the first group 3. One possible reason for scientists to make experiments with rats or other animals is that _________. A) rats benefit from the experiments B) the experiments can boost the brains of the rats C) an effect found in rats may also apply to humans D) rats and humans are very much alike 4. Which word in Paragraph 6 tells us that older adults were divided into groups in the human studies? A) Corresponding. B) Inactive. C) Older. D) Faster. 5. Which of the following is not a finding that results from the studies of older adults? A) Regular exercise can improve the speed with which the brain processes information. B) Inactive adults can hit buttons faster in response to a tone after being trained. C) Getting old is the cause for the reduction in mental function. D) Exercise can make one smarter.大学英语(二)

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