【练习】
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.