填空题

When you walk into a National Forest, you really believe you’re the first person who’s ever been here. Funny thing is, you’re not.
These forests have been used for over a hundred years. From this timber stand (堆木场), settlers used wood to build their homes. And ties (枕木) were cut for the railroad. Hard to believe, isn’t it But that’s the Miracle of the Forest. With careful management these forests have renewed themselves, year after year providing us with all kinds of benefits. And that’s why we call them "Forever Forests".
Come to see for yourself! And get involved with the new "forests for us" program and tell people all about the Miracle of the Forest.
For more information, write: Forest for Us, P. O. Box 2000, Washington, DC 20013.
Miracle of the Forest
In addition to many other things, the National Forests have provided (46) for the building of houses, and (47) for the railroad.
The National Forests have renewed themselves because of (48) and so they are now called (49) . This advertisement invites readers to join in the program of (50) .