Scientists have long believed one way to stop the Earths atmosphere from warming is by planting more trees.The idea is that more trees will 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 Earths 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.

　　The findings of the two studies were published last month in Nature magazine. They suggest there is limited value in planting trees to reduce the carbon dioxide pollution in the atmosphere.

　　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 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 researchers put trees in extra carbon dioxide in the first study?

　　A) To learn whether trees can still absorb carbon dioxide under extreme conditions.

　　B) To get more oxygen from these trees.

　　C) To evaluate the maximum carbon dioxide that 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 content was mainly absorbed in the soil.

　　D)They absorbed more carbon dioxide.

　　4.Scientist Ram Oren is of the opinion that common beliefs of the trees ability to absorb carbon dioxide are____.

　　A) biased B) insightful

　　C) overoptimistic D) totally wrong

　　5.The word it probably refers to ____.

　　A) carbon dioxide B) nitrogen

　　C) atmosphere D) coal

　　答案与解析：

　　1.A。本文主要介绍了一些科学家提出的关于树林与二氧化碳关系的新学说。主题题。B),D)均与本文无关;C)则由于实验显示树木吸收并不那么有效，因此从本文观点来看正好错误。

　　2.D。研究者把树木放入过量二氧化碳的环境中研究树木相应的生长规律。细节推理题。关键语句： 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. 可以看出是研究生长规律.A),B),C)均和本文无关。

　　3.B。在第二个试验中落下的树叶分解后,包含的主要碳成分转化为二氧化碳?？凸凼率堤狻９丶锞洌?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. 而A), C), D) 均错误。

　　4.C?？蒲Ъ襌am Oren认为大众对树叶作用的观点过于乐观。态度判断题。关键语句： He says that earlier estimates on the ability of forests to absorb carbon dioxide were overly hopeful. 可见他认为普通观点过于乐观。

　　5.A。对应段落里的 it 指二氧化碳。词意判断题。关键语句： 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. 可见应是二氧化碳.其余选项与本段无关。

　　Scientists have long believed one way to stop the Earths atmosphere from warming is by planting more trees.The idea is that more trees will 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 Earths 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.

　　The findings of the two studies were published last month in Nature magazine. They suggest there is limited value in planting trees to reduce the carbon dioxide pollution in the atmosphere.

　　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 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 researchers put trees in extra carbon dioxide in the first study?

　　A) To learn whether trees can still absorb carbon dioxide under extreme conditions.

　　B) To get more oxygen from these trees.

　　C) To evaluate the maximum carbon dioxide that 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 content was mainly absorbed in the soil.

　　D)They absorbed more carbon dioxide.

　　4.Scientist Ram Oren is of the opinion that common beliefs of the trees ability to absorb carbon dioxide are____.

　　A) biased B) insightful

　　C) overoptimistic D) totally wrong

　　5.The word it probably refers to ____.

　　A) carbon dioxide B) nitrogen

　　C) atmosphere D) coal

　　答案与解析：

　　1.A。本文主要介绍了一些科学家提出的关于树林与二氧化碳关系的新学说。主题题。B),D)均与本文无关;C)则由于实验显示树木吸收并不那么有效，因此从本文观点来看正好错误。

　　2.D。研究者把树木放入过量二氧化碳的环境中研究树木相应的生长规律。细节推理题。关键语句： 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. 可以看出是研究生长规律.A),B),C)均和本文无关。

　　3.B。在第二个试验中落下的树叶分解后,包含的主要碳成分转化为二氧化碳?？凸凼率堤狻９丶锞洌?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. 而A), C), D) 均错误。

　　4.C?？蒲Ъ襌am Oren认为大众对树叶作用的观点过于乐观。态度判断题。关键语句： He says that earlier estimates on the ability of forests to absorb carbon dioxide were overly hopeful. 可见他认为普通观点过于乐观。

　　5.A。对应段落里的 it 指二氧化碳。词意判断题。关键语句： 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. 可见应是二氧化碳.其余选项与本段无关。