1 . Burning coal for energy adds planet-warming carbon dioxide(CO2) to Earth's atmosphere. As the planet heats up, experts warn that simply cutting greenhouse gas emissions（排放） will not be enough to avoid global warming. CO2 must also be remcved from the atmosphere.
Existing experimental machines that pull CO2 directly from the air are too expensive to be widely used. But a new effective technology to remove CO2 already exists. It is not expensive and easy. It is forests. Planting trees and watching forests are effective ways to clean the air.
Forests used to cover large areas of the Appalachian Mountains in the eastern United States. In the state of West Virginia, coal mining left the land there bare, without trees. Over the years, coal mining and cutting forests took over 90 percent of the red spruce（云杉） forests.
Chris Barton works for the University of Kentucky. He started a group called Green Forests Work, aiming to put trees back on the roughly 400 , 000 hectares of land.
However, Barton explains the land has problems. "If you planted trees on these places, they just didn't grow. The ground was too hard. Water didn't infiltrate（渗透）. The trees can't root. Oxygen can't circulate in those environments. "Using heavy equipment, workers tear the ground. In this way, the trees put down roots.
Barton says not everyone believes the solution is a good idea. "We've had a lot of doubtful look at us twice from people. But after we do it, there's no question that it was the right thing to do. "And it has worked. Forests are coming back to the grounds.
Scientists say that, in West Virginia alone, restoring red spruce forests to the area could send what is equal to 56 million barrels（桶）of oil into the ground. But it will take time—a long time. Around the world, experts say, nature offers powerful tools to fight climate change. But patience is needed. Nature works, but slowly, in its own time.
1. What is the economical and effective way to remove CO2 from the air?| A．Inventing new and powerful machines. | B．Cutting greenhouse gas emissions. | C．Making use of natural gases instead of coal. | D．Planting trees and protecting forests. |
| A．Cry. | B．Repair. | C．Destroy. | D．Cover. |
| A．oxygen is not enough for trees to grow there |
| B．too many rocks had made it hard to plant trees |
| C．coal mining has spoiled the land through years |
| D．there is no water for trees to grow there |
| A．a painful process | B．a slow process | C．a creative process | D．a learning process |
