1 . Directions: Fill in each blank with a proper word chosen from the box. Each word can only be used once. Note that there is one word more than you need.
A. countless B. exhausted C. comparison D. essential E. estimates F. features
G. relatively H. cleared I. unfortunately J. recycled K. restricts |
Rain forests, found in Earth's temperate and tropical zones, are some of the most biologically varied ecosystems on the planet. All rain forests share certain 1 , including a closed canopy, the dense vegetation of the top branches that forms a roof above the forest floor, a damp and warm climate, and 2 constant temperatures throughout the year. Most of the forest's insect and animal life grows well in the canopy's leafy and sunlit environment. The forest's ground cover, by comparison, is small. Less than 2 percent of the sun's light makes its way through the canopy and the darkness below. This darkness, along with the poor quality of the soils, 3 plant growth.
Rain forests are a(n) 4 part of Earth's total ecology. Huge amounts of water are absorbed into tree roots and 5 into the atmosphere from the tree leaves through a process called transpiration（蒸发）. Tree roots also fix the soil in place and slow the runoff of rains into rivers and oceans. Through the process of photosynthesis（光合作用）, rain forests absorb more carbon dioxide and give off more oxygen than any other ecosystem.
The rain forests are 6 shrinking at a rapid rate as a result of the profitable ventures of farming, logging, and mining. When tropical rain forests are 7 in order to raise cattle and crops, the nutrient-poor soils are quickly 8 . When farmers move on to new areas heavy rains and baking sun leave the land fruitless and lifeless. Logging and mining cause similar damage to the land and destroy the territory of 9 millions of birds, insects and animals. By some 10 an area of tropical rain forest the size of the state of Delaware disappears in this way every month.
