填空题 In 1620, about half the USA was 1 forests. Today the forests have almost gone. A lot of good land has 2 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 the 3 part of our country. The Great Green Wall is 7,000 kilometers long, and between 400 and 1,700 kilometers 4 . It will stop the wind from blowing the earth away. It will stop the sand from moving towards the 5 farmland in the south.