June 5 is World Environment Day. This makes us pay more attention to our environment and the need to protect it. When Wang Boxuan, a Beijing high schoolboy, uses up his exercise books, he does not throw them away. Each one is stored at his school with hundreds of exercise books given by other students. Then they are sold to a Beijing paper making factory. The paper is recycled and used again by students and teachers in the school. At the same time, the money made from the sales goes towards schools in Inner Mongolia for planting trees and grass. This place is one of the sources of the sandstorms that often attack Beijing during springtime. Wang's school is one of the schools in the capital that take part in the "Green Promise" --environmental protection activity. So far, nearly 210,000 students have taken part in the activity, collecting more than 87 tons of waste paper. Students are eager to help make the capital a more pleasant place. Which is the best title for the passage?
Planting Trees. Green Promise. Collecting Waste Paper. Making Money.