[简答题] The Forest Service is responsible for the forests on public lands in the United States. It supervises almost seventy-eight million hectares of forests, grasslands, rivers and lakes. It is an agency of the Department of Agriculture. Forest Service officials say there are four major threats to forests and wild lands in America. The first is the threat of fire and fuel. This year, forest fires have burned more than three million hectares of land. That is almost two times as much as the ten-year average. Fires are a natural part of forest growth, but they can also threaten lives and property. Fuel is dead plant material and small plants that grow under tall trees. As much as forty-nine metric tons of fuel can build up on every hectare of forest floor. The Forest Service estimates that up to one-fourth of the forests it supervises have dangerous levels of fuel. Sometimes foresters set controlled fires to remove the fuel. Other times the fuel must be cleared by hand. Another threat