共用题干题

< p>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 < span style="text-decoration:underline;">21< /span>formerly occupied by forests，deserts，and wetlands．< span style="text-decoration:underline;">22< /span>the beginning of European settlement in America，< span style="text-decoration:underline;">23< span style="text-decoration:underline;">，< /span>< /span>over 65，000，000acres of wetlands have been drained．One million acres alone vanished < span style="text-decoration:underline;">24 < /span>1985and 1995．< br/>Habitat destruction can be 25or it can be subtle，occurring over a < span style="text-decoration:underline;">26< /span>period of time without being noticed．< span style="text-decoration:underline;">27< /span>such as sewage from cities and chemical runoff fromfarms，can change the < span style="text-decoration:underline;">28< /span>and quantity of water in streams and rivers．To < span style="text-decoration:underline;">29< /span>living in a delicately balanced habitat，this disturbance can be as< span style="text-decoration:underline;">30< /span>as the clear-cutting of a rainforest．< br/>< span style="text-decoration:underline;">31< /span>remaining habitats are carved into smaller and smaller pockets or islands，remaining species are forced to exist in these < span style="text-decoration:underline;">32< /span>areas，which causes further habitat < span style="text-decoration:underline;">33< /span>These species become less adaptable to environmental < span style="text-decoration:underline;">34< /span>；in fact，they become < span style="text-decoration:underline;">35< /span>endangered．Scientists believe that when a habitat is cut by 90%，one-half of its plants，animals and insects will become extinct．< /p>

33处应填（）。