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听力原文： Electronic Commerce or e-commerce refers to the exchange of goods and services by means of the Internet or other computer networks. E-commerce follows the same basic principles as traditional commerce-that is, buyers and sellers come together to exchange goods for money. But rather than conducting business in the traditional way-in mores or through mail order catalogs and telephone operators-in e-commerce buyers and sellers do business over networked computers.
E-commerce offers buyers convenience. They can visit the World Wide Web sites of multiple sellers 24 hours a day and seven days a week to compare prices and make purchases, without having to leave their hones or offices. In some eases, consumers can immediately obtain a product or service, such as an electronic book, a music file, or computer software, by downloading it over the Internet.
For sellers, e-commerce offers a way to cut costs and' expand their markets. They do not need to build staff, or maintain a store or print and distribute mall order catalogs. Because they sell over the global Internet, sellers have the potential to market their products or services globally and are not limited by the physical location of a store.
E-commerce also has some disadvantages, however. Consumers are reluctant to buy some products online. Online furniture businesses, for example, have failed for the most part because customers want to test the comfort of an expensive item such as a sofa before they purchase it. Many people also consider shopping a social experience. For instance, they may enjoy going to a store or a shopping mall with friends or family. Consumers also need to be reassured that credit card transactions are secure and that their privacy is being respected.
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Tropical rainforests comprise only 40% of the world's tropical forests and only 20% of the
Rain forests
Did you know there are two types of Rainforest-the temperate and the tropical？ Tropical rainforests are found close to the equator. Temperate rainforests are found along coasts in the temperate zone, such as the Pacific Northwest of the USA. Both are endangered!
Rainforests Endangered!
Today only about three percent of the original temperate rainforest in the U. S. A. remains, mostly inside Olympic National Park in Washington State. Prior to the arrival of homesteaders just over a century ago, the Olympic Peninsula contained more than a million acres of old-growth spruce and hemlock. Because of habitat destruction, many plants and animals have become "island dwellers" inside the park now.
Tropical rainforests comprise only 40% of the world's tropical forests and only 20% of the world's total forests. They cover 6%-7% of the Earth's land surface. Half of the world's plant and animal species live in the tropical rainforests of the world. Thirty acres of trees are cut in the tropical rainforests every minute. As you read this, tropical rainforests are shrinking. Each second a portion of rainforest the size of a football field is destroyed or damaged.
What Makes the Tropical Rainforest Special？
The rainforests are home to half of the Earth's plant and animal species.
They are winter homes to many birds that breed in temperate latitudes.
Tropical rainforests are some of the most beautiful wildernesses on our planet.
They are home to tribal cultures that have survived successfully in the forests for many thousands of years.
The forests are a potential source of medicinal plants that may benefit everyone on Earth.
The ecosystem of the rainforest is based on the most complex interdependence of plants and animals. This is both the forest's strength and its weakness: highly specialized organisms are particularly vulnerable to disturbance, because they cannot adapt fast enough to survive the change.
Tropical rainforests help maintain global rain and weather patterns. Much of the water that evaporates from the trees returns in the form. of rainfall. Removal of the forest can change the natural rainfall patterns.
Tropical Rainforest Layers
Tropical rainforests have four layers:
Emergent Layer
These giant trees thrust above the dense canopy layer(树冠层) and have huge mushroom-shaped crowns. These trees enjoy the greatest amount of sunlight but also must endure high temperatures, low humidity, and strong winds.
Canopy Layer
The broad, irregular crowns of these trees form. a tight, continuous canopy 60 to 90 feet above the ground. The branches are often densely covered with other plants (epiphytes) and tied together with vines (lianas). The canopy is home to 90% of the organisms found in the rain forest; many seeking the brighter light in the treetops.
Understory
Receiving only 2%-15% of the sunlight that falls on the canopy, the understory is a dark place. It is relatively open and contains young trees and leafy herbaceous plants that tolerate low light. Many popular house plants come from this layer. Only along rivers and roadways and in tree fall and cut areas is sunlight sufficient to allow growth to become thick and impenetrable
Forest Floor
The forest floor receives less than 2% of the sunlight and consequently, little grows here except plants adapted to very low light. On the floor is a thin layer of fallen leaves, seeds, fruits, and branches that very quickly decomposes. Only a thin layer of decaying organic matter is found, unlike in temperate deciduous(落叶性的) forests.
Soil and Nutrient Recycling
Most tropical rainforest soils are relatively poor in nutrients.
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