单选题 .  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     1    formerly occupied by forests, deserts, and wetlands.     2    the beginning of European settlement in America,     3    , over 65,000,000 acres of wetlands have been drained. One million acres alone vanished     4    1985 and 1995.
    Habitat destruction can be     5    or it can be subtle, occurring over a     6    period of time without being noticed.     7    such as sewage from cities and chemical runoff fromfarms, can change the     8    and quantity of water in streams and rivers. To     9    living in a delicately balanced habitat, this disturbance can be as     10    as the clear-cutting of a rainforest.
        11    remaining habitats are carved into smaller and smaller pockets or islands, remaining species are forced to exist in these     12    areas, which causes further habitat     13    . These species become less adaptable to environmental     14    ; in fact, they become     15    endangered. Scientists believe that when a habitat is cut by 90%, one-half of its plants, animals and insects will become extinct.1.