In 1620, about half the USA was (11) forests. Today the forests have almost gone. A lot of good land has (12) them, leaving

In 1620, about half the USA was covered by forests. Today the forests have almost gone. A lot of good land has gone with them, leaving only sand. China doesn’t want to copy the USA’s example. We’re planting more and more trees. We’ve built the "Great Green Wall" of trees across northern part of our country. The Great Green Wall is 7,000 kilometers long, and between 400 and 1,700 kilometers wide. It will stop the wind from blowing the earth away. It will stop the sand from moving towards the rich farmland in the south.