今年天津市的专升本考试觉得简单还是难？？

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22题的答案是（ ）

A.At
B.Before
C.After
D.Since

生产方式是（ ）

A.地理环境和人口因素的统一
B.社会存在和社会意识的统一
C.经济基础和上层建筑的统一
D.生产力和生产关系的统一

A.2y3
B.6xy2
C.6y2
D.12xy