建议用时：15分钟
A
[2015·重庆一中一诊]The African elephant, the largest land animal remaining on earth, is of great importance to African ecosystem (生态系统). Unlike other animals, the African elephant is to a great extent the builder of its environment. As a big plant-eater, it largely shapes the forest-and-savanna (稀树草原) surroundings in existence for millions of other animals that live in its habitat (栖息地)．
It is the elephant's great desireW2W1P2P1 for food that makes it a
Sdisturber of the environment and an important builder of its habitat.
In its continuous search for the 300 pounds of plants it must have every day, it kills small trees andunderbushes, and pulls branches off big trees. This results in numerousopen spaces in both deep tropical forests and in the woodlands that cover part of the African savannas. In these open spaces are numerous plants in variousstages of growth that attract a variety of other plant eaters.
Take the rain forests for example. In their natural state, the spreading branches overhead shut out sunlight and prevent the growth of plants on the forest floor. By pulling down trees and eating plants, elephants make open spaces, allowing new plants to grow on the forest floor. In such situations，the forests become suitable for large hoofed plant eaters to move around and for small plant eaters to get their food as well.
What worries scientists now is that the African elephant has become an endangered species. If the elephant disappears, scientists W4P3W3
www.99jianzhu.com/包含内容：建筑图纸、PDF/word/ppt 流程，表格，案例，最新,免费下载,施工方案、工程书籍、建筑论文、合同表格、标准规范、CAD图纸等内容。