【練習】

Dinosaurs, saber-tooth tigers and the dodo bird are famous examples __1

of animals that have become extinct. In case of the dinosaurs, it __2

seems likely that a catastrophic event alters the global climate __3

enough to lead to their disappearance. More recent extinctions　and near-extinctions－such as the blue whales, tiger, panda, and __4

North American bison—have been the direct result of human activity. By the early 1990s, species were becoming extinct at a rate of three per hour, or 27,000 every day – a figure quoted by the American biologist Edward O.Wilson of Harvard University, based on his　most conservative estimates. This rate of extinctions carries with　it some terrible consequences. Each plant that becomes extinct,for example, may take with it as much as 30 insects and animals __5

that depend on it for food. Habitat loss is one of the most important causes of extinction. For rising populations in many countries __6

lead to the clearing of more land, habitats such as raining forest __7

and grasslands disappear.

In the East Africa, once renowned for its wildlife, few wild animals __8

remain living outside the boundaries of national parks and game __9

reserves. In other parts of the world, coastal ecosystems are clearing __10

for development. Wetland areas are drying out as a result of water extraction to support farming and tourism. Bird species are among　the worst affected by the loss of wetlands.

（責任編輯：liushengbao）