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Wind energy has been praised as cost-effective to produce clean energy as well as jobs. That promise, along with new government subsidies (补贴), has helped wind turbines (涡轮机) pop up on hills and fields throughout Americ

a. But not every environmentalist is happy about that development. Critics charge that wind-energy development can cause habitat fragmentation-a displacement of a species that can eventually reduce its numbers-as well as the deaths of birds and bats (a species that is especially vulnerable due to its low reproductive rates) that collide with the wind turbines’ massive blades. A 2007 study by the National Academy of Sciences puts the number of birds killed each year at about 20,000 to 30,000. That’s a low estimate, says Michael Fry of the American Bird Conservancy. According to his group, turbines kill three to 11 birds per megawatt of wind energy they produce.
According to critics, wind-energy development may causeA. the deaths of 20,000 to 30,000 birds.B. distinction of many species in the area.C. habitat fragmentation and deaths of birds.D. environment recovery from destruction.

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单项选择题

Wisdom in old age depends on a fresh supply of new brain cells, a study in mice suggests.. When mature mice learn a new task, their newly generated brain cells are three times more active than their old ones, the researchers found. The findings add to a growing body of evidence that the adult brain needs a steady addition of new cells to maintain its mental faculties. Researchers found that mature mice’s brain cells are much more active than before when

A. they are transplanted with new brain cells.
B. they learn to do something new.
C. they gain weight in the body.
D. they get new cells from other mic

单项选择题

The eight pilot projects funded by $47 million of the Department of Energy’s stimulus money are located in different regions of the country from Hawaii to Massachusetts. The department hopes the projects will uncover which devices or systems work best. But again, the question of success could vary depending on the area and its consumers. In rural towns, smart-grid technology may mean creating a system in which homes and businesses receive electricity without interruption. In windy Colorado, a smart grid may focus more on harnessing wind energy to supplant (取代, 代替) electrical power. In rural areas, smart-grid technology focuses on

A. creating a system that could be set as an example for all smart grids.
B. making use of wind energy to replace electrical power.
C. supplying electricity to homes and businesses without interruption.
D. the efficiency when transmitting electricity for long distances.