Question

Scientists have long believed one way to stop the Earth’s air from warming is by planting more trees. The idea is that more trees will take in or absorb(吸收) some of the CO₂ in the air. CO₂ is a gas released by cars, factories and other human activities. The gas traps heat in the Earth’s air, which warms the planet. However, two new studies have found that trees may not be as helpful in reducing CO₂ as thought.

The first study was done at Duke University in Durham, North Carolina. Researchers pumped(打气) extra CO₂ into a test area where green 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(营养素), such as nitrogen(氮).

In the second study, researchers from Duke and Bowdoin College in Brunswick, Maine examined the soil(泥土) 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 let into the air as CO₂.

The findings of the two studies were published last month in Nature magazine. They suggest there is limited(有限的) value in planting trees to reduce the CO₂ pollution in the air.

Forest planting has been a part of negotiations(谈判) on a world agreement to reduce greenhouse gases that scientists believe cause global warming. The United States, Canada, Japan and some other countries have supported the idea. But this new research suggests the idea is not as effective as environmental activists(积极分子) had thought. Scientist Ram Oren of Duke University led the study on tree growth. He says that earlier estimates(估计) on the ability of forests to absorb CO₂ were overly hopeful.

Some other scientists say the research provides some of the first evidence on how trees react(反应) to CO₂. Some other scientists say the research disputes(质疑) a belief among some coal and power companies. The companies say that more CO₂ in the air will not create harmful global warming. Instead, they say it will increase forests and other plants.

1.Why did the researchers put trees in extra CO₂ in the first study?

A. To learn whether trees can still absorb CO₂ under extreme conditions.

B. To get more oxygen from these trees.

C. To know how much CO₂ that trees can absorb.

D. To see the effect of CO₂ on the growth rate of these trees.

2.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 had mainly turned into CO₂.

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

D. They absorbed more CO₂.

3.Scientist Ram Oren thinks that common beliefs of the tree’s ability to absorb CO₂ are __________.

A. just right          B. not acceptable

C. a bit too cheerful  D. too dangerous

Answer

1.D

2.B

3.C

【解析】

试题分析：这篇短文主要讲述了长期以来科学家都认为多种植树木可以阻止大气变暖，然而文章通过两个实验，表明树木并不像我们想象的那样有助于减少二氧化碳。文章还介绍了由这两个实验引发的科学争论。

1.D细节理解题。根据短文“Researchers pumped(打气) extra CO2 into a test area where green 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. ”的描述可知，在第一个实验中，研究者把树木置于特殊的二氧化碳中是为了验证二氧化碳对树木生长率的影响。结合选项可知应选D。

2.B细节理解题。根据短文“They discovered that as the leaves broke down into the soil, all the carbon was not trapped in the soil. Much of it was let into the air as CO2.”的描述可知，在第二个实验中，落叶腐烂以后大部分转化成二氧化碳。结合选项可知应选B。

3.细节理解题。根据短文“Scientist Ram Oren of Duke University led the study on tree growth. He says that earlier estimates(估计) on the ability of forests to absorb CO2 were overly hopeful.”的描述可知，对树木吸收二氧化碳的早期估计期望过高。结合选项可知应选C。

考点：环保类短文阅读。