题目内容：

七选五根据短文内容，从短文后的七个选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

It is said that farmers or peasants, especially those in developing countries, are often criticized for cutting down forests. But a new study suggests that many farmers recognize the value of keeping trees.Researchers using satellite images found at least ten percent trees cover on more than one billion hectares of farmland.1.. Earlier estimates were much lower but incomplete. The authors of the new study say it may still underestimate the true extent worldwide.The study found the most trees cover in South America.2.. North Africa and West Asia have the least.The study found that climate conditions alone could not explain the amount of trees cover in different areas.3.. There are areas with few trees but also few people, and areas with many trees and many people. The findings suggest that things like land rights, markets or government policies can influence tree planting and protection.Dennis Garrity heads the World Agroforestry Center.4.. The problem, he says, is that policy makers and planners have been slow to recognize this and to support such efforts.The satellite images may not show what the farmers are using the trees for, but trees provide nuts, fruit, wood and other products.5.. Even under drought (干旱) conditions, trees can often provide food and a way to earn money until the next growing season.Some trees act as natural fertilizers. They take nitrogen (氮气) out of the air and put it in the soil. Scientists at the Center say the use of fertilizer trees can reduce the need for chemical nitrogen by up to three-fourths. Trees also capture carbon dioxide, a gas linked to climate change.

A.Nor could the size of nearby populations, meaning people and trees can live together.

B.He says farmers are acting on their own to protect and plant trees.

C.Almost all of it is covered by trees.

D.They also help prevent soil loss and protect water supplies.

E.He devotes most of his time to making people realize its importance.

F.That is nearly half of the farmland in the world.

G.Next comes Africa south of the Sahara, followed by Southeast Asia.