The soil is a part of the earth，　　 is the atmosphere．

　 A．that　　　 B．such　　　 C．so　　　 D．it

 The atmosphere is as much a part of the earth as ________ its soil and water of its

      lakes，rivers and oceans.

      A．has              B．do       C．is                D．are

There are several advantages in planting trees：they firm the soil，soak(渗透) up extra water and take carbon dioxide out of the atmosphere. However，it now turns out that planting trees could add to global warming. We all know that tree roots do a great job of keeping soil firmly on the ground and out of the wind's power. The problem is that some of the dust clouds play an important part in soaking up carbon dioxide.

Huge dust storms blow out over the oceans from  dry parts of North Africa and Central Asia. Tons of dust are lifted and left as a thin film over the ocean surface.

Dust from China is carried east and left in the Pacific Ocean. If a tree­planting programme there is successful and the dust supply reduced, the net result may be that less carbon dioxide gets locked away in the ocean.

Andy，an environmental scientist has spent the past few years studying dust and says his work shows clearly the complexity of the system. For this reason the need is to focus on cutting carbon dioxide giving off rather than doing anything else.

Robert, an American scientist, has  shown that when native grassland areas are invaded by trees, carbon is lost from the soil. “We are studying why the soil carbon disappears，but one theory is that trees do a lot more of their growing above ground compared to grass, so less carbon goes directly into the soil from trees.” said Robert.

In wet areas of the world, the gain from trees absorbing carbon dioxide above ground seems to be outweighed by the loss of carbon from the soil below ground.

Countries that plan to fight against global warming by planting trees may have to think again. Solutions to environmental problems are often more complex than they first appear，and understanding the Earth's climate is a very great challenge.

60．People usually hold the opinion that ________.

A. huge dust storms can destroy carbon dioxide

B. planting trees could reduce global warming

C. huge dust storms can destroy the oceans on the Earth

D. planting trees is the only way to control huge dust storms

61．Andy, an  environmental  scientist, believes  that________.

A. environmental problems are more complex than expected                 

B. trees shouldn't have been planted in dry places

C. dust plays a more important part than trees

D. carbon dioxide is harmful to everything

62．Robert's experiment proves that ________.

A. trees absorb more carbon than grass

B. carbon can turn grass into dust

C. less carbon can make trees grow faster

D. grassland areas should be covered by forests

63．The best title for this passage is “________”．

A. The importance of planting trees

B. The dust clouds soak up carbon dioxide

C. Is it really useful to plant trees to reduce global warming?

D. Why the soil carbon disappears

Scientists have long believed one way to stop the Earth’s atmosphere from warming is by planting more trees. The idea is that more trees take in or absorb some of the carbon dioxide in the atmosphere. Carbon dioxide is a gas released by cars, factories and other human activities. The gas traps heat in the Earth’s atmosphere, which warms the planet. However, two new studies have found that trees may not be as helpful in reducing carbon dioxide as had been thought.

The first study was done at Duke University in Durham, North Carolina. Researchers pumped extra carbon dioxide into a test area where pine trees were growing. The trees grew thirty-four percent faster during the first three years. However, in time, the trees slowed to about their normal growth rate. The scientists say this is because trees need other nutrients, such as nitrogen.

In the second study, researchers from Duke and Bowdoin College in Brunswick, Maine examined the soil around trees. They discovered that as the leaves broke down into the soil, all the carbon was not trapped in the soil. Much of it was released into the atmosphere as carbon dioxide.

Forest planting has been a part of negotiations on a world agreement to reduce greenhouse gases that scientists believe cause global warming. The United States, Canada, Japan and some other industrial countries have supported the idea. But this new research suggests the idea is not as effective as environmental activists had thought. Scientist Ram Oren of Duke University led the study on tree growth. He says that earlier estimates on the ability of forests to absorb carbon dioxide were overly hopeful.　　

Some scientists not involved in the studies say the research provides some of the first evidence on how trees react to carbon dioxide. Other scientists say the research disputes（对……质疑） a belief among some coal and power companies. The companies say that rising levels of carbon dioxide in the atmosphere will not create harmful global warming. Instead, they say it will increase forests and other plants.

1．What is the purpose of this passage？

A．Introduce some new ideas about the relationship between trees and carbon dioxide.

      B．Introduce recent condition of global industrial pollution.

      C．Call on people to plant more trees to reduce greenhouse gases.

   D．Point out that power companies should be responsible for the rising levels of carbon

dioxide.

2．Why did the researchers do the TWO studies?

A．To prove that trees may not be as helpful in reducing carbon dioxide as had been thought.

B．To get more oxygen from these trees.

C．To evaluate（评价，评估）the maximum carbon dioxide the trees can absorb

D．To see the growth rate of these trees.

3．What happened to the leaves falling from the trees in the second study？

A．They broke down and the main parts turned into oxygen.

      B．They broke down and the carbon content had mainly turned into carbon dioxide.?

C．They broke down and the carbon dioxide content was mainly absorbed in the soil.

      D．They absorbed more carbon dioxide.?

4．Scientist Ram Oren is for the opinion that common beliefs of the tree’s ability to absorb carbon dioxide are             .

       A．based                  B．insightful             C．overoptimistic      D．totally wrong

5．The word “it” in the last paragraph probably refers to           .

       A．carbon dioxide     B．nitrogen               C．atmosphere          D．coal