Wind power is booming， largely due to a search for energy from sources other than fossil fuels， such as petroleum and coal. Much of today's wind power comes from big "farms" that have many tall， modern windmills， called wind turbines. These machines have long shafts. In some designs， they can reach taller than a 10-story building. These shafts are topped by giant blades. These connect to a generator that converts the energy of their spinning motion into electricity.

But some people， even those very concerned about the effects of fossil fuels on the environment， have growing concerns about wind power. The turbine farms are taking up a growing fraction of the landscape. Plus， to tap the speedier winds found at higher altitudes， the blades have been growing longer and sitting atop ever-higher shafts. These trends pose increasing threats to wildlife.

Turbine blades strike and kill flying animals each year， including bats and migrating birds. For instance， an estimated 214000 to 368000 small perching birds， many of them songbirds， may be killed by turbine blades each year. That's the conclusion of a study. That might sound like a lot of birds. But about 5 billion of those types of birds live or breed in North America. This means that the fraction killed by wind turbines is really tiny. It also pales in comparison to the nearly 7 million birds that are estimated to die each year after flying into other tall structures， such as radio towers and cell-phone towers， the study's authors point out.

Other critics think that the forests of turbines are just plain ugly. And many people who live near wind farms complain about the whooshing noise made by the rapidly whirling blades.

Some engineers are now investigating a seemingly radical solution - one that might solve many of these problems. They'd like to take the earthbound wind turbines and fly them far above the ground. They could be held in place by kites or helium-filled blimps and connected to the ground by long tethers. High above - and possibly out of the flight paths of some birds and bats - they would be largely out of sight and too high for their noise to bother anyone.

Placed in the path of steady and speedy winds， such airborne turbines could generate huge amounts of power， analyses now suggest. And doing so might not cost any more than operating wind turbines on the ground. But first， researchers will need to figure out how to tap into that sky-high energy and bring it safely to the ground.

1. Which of the following does not describe how wind turbines work？ ____.

A. The wind makes the blades spin around

B. The blades capture energy from the wind

C. A generator converts the energy of the spinning motion into electricity

D. The long shafts are anchored to the ground

2. Why are there growing concerns over wind power？ ____.

A. Because wind power is an exhaustible source of energy

B. Because turbine farms pose increasing threats to wild life

C. Because turbine farms are taking up more and more farmers' land

D. Because wind power production is subject to seasonal variations

3. What are the main problems of operating wind turbines on the ground？ ____.

a. threats to wild life b. carbon emission

c. visual pollution d. noise pollution

A. abc B. bcd C. acd D. abcd