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

A improvements  

B changes   

C protection  

D development