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The destruction of habitats（栖息地）all over the world is the primary reason species are becoming extinct（灭绝）or endangered．Houses，highways，dams，industrial buildings，and ever-spreading farms now dominate 21formerly occupied by forests，deserts，and wetlands．22the beginning of European settlement in America，23，over 65，000，000acres of wetlands have been drained．One million acres alone vanished 24 1985and 1995．
Habitat destruction can be 25or it can be subtle，occurring over a 26period of time without being noticed．27such as sewage from cities and chemical runoff fromfarms，can change the 28and quantity of water in streams and rivers．To 29living in a delicately balanced habitat，this disturbance can be as30as the clear-cutting of a rainforest．
31remaining habitats are carved into smaller and smaller pockets or islands，remaining species are forced to exist in these 32areas，which causes further habitat 33These species become less adaptable to environmental 34；in fact，they become 35endangered．Scientists believe that when a habitat is cut by 90%，one-half of its plants，animals and insects will become extinct．

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