Forests are the lungs of the earth．Without them，it cannot breathe．It needs its forests to remove carbon dioxide from the air and to make oxygen．In many countries，such as New Zealand，Canada，and Brazil，forests were cut down to（1） （提供）wood to build houses．Cutting down trees is（2）h to human beings，animals and plants． Many young volunteers around the world are working in their holidays to plant new trees to replace them．
These young men and women（3）f many difficulties when they plant new tees．The weather may be very hot and dry or may be very cold and wet．Tree（4） （种植者）are changing the world．They plant different types of trees so that birds and animals can live in the forests．They（5）b that in 50 years their little trees will become beautiful forests．