(流失) into streams, thus cutting down on pollution and improving the soil. Second, trees provide firewood. So many trees have been cut down in Africa that women must walk far from home to find wood for cooking. New trees can also keep deserts from spreading.

　　Dr. Maathai's Green Belt Movement pays local women for every tree they plant that is still alive three months later. In its first 15 years, the Green Belt Movement employed at least 50,000 women and planted more than 10 million trees. Following Dr. Maathai's example, the Kenyan government increased its own tree-planting efforts. The movement has spread to 30 countries in Africa.

　　When the land and people's lives have improved, Dr. Maathai says, peace will follow.

21. The underlined word "conserve" in Paragraph 2 probably means "_____".

A. use B. protect

C. find D. provide

22. Dr. Wangari Maathai is the first African woman to _____.

A. win the Nobel Peace Prize

B. encourage people to plant trees

C. get a master's degree in science

D. realize the power of knowledge

23. What's Paragraph 4 mainly about?

A. The importance of trees.

B. How trees prevent pollution.

C. How planting trees works in Africa.

D. The history of tree-planting in Africa.

24. The Green Belt Movement _____.

A. aims to provide job opportunities for women

B. attracted the world's attention to Africa

C. pays for every newly-planted tree

D. covered a large area in Africa