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(打氣) 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(營養(yǎng)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(談判) 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(積極分子) had thought. Scientist Ram Oren of Duke University led the study on tree growth. He says that earlier estimates(估計) 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(反應) to CO2. Some other scientists say the research disputes(質疑) 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