[单项选择]By the first decade of the 21st century, international commercial air traffic is expected ______beyond today's levels.
A. to have extended
B. to be extending
C. being extended
D. having been extended

[单项选择]The population in the 21st century according to the writer ______.
A. will be smaller than a fw years ago
B. will not be as small as people expect
C. will prove to be a threat to the world
D. will not consitute as serious a problem as expected

[单项选择]The 21st Century is different from the other three schools in that ______.
A. its teaching quality is better
B. it is nearest to the city centre
C. its courses are more advanced
D. it requires an entrance examination

[单项选择]Since the beginning of the 21 st century, the government has started ______.
A. a plan to produce more milk
B. a plan to offer milk to school children
C. to produce milk for more people
D. to ask schools to offer milk

[单项选择]

As we enter the 21st century, a new global economy draws nations ever closer. But our growing interdependence (21) on much more than technology and trade. For we are linked intrinsically by the physical and biological webs that (22) life on our planet -- and, increasingly, by the threat of their unraveling. Indeed, (23) we reach across borders and face this threat together, the next century may (24) an Earth in ecological crisis, with half of all (25) gone, and our grandchildren enduring deadly floods, drought and disease (26) by global warming.
When millions across America (27) the first Earth Day 30 years ago, our focus understandably was our own backyard. Our rivers were (28) on fire, and our skylines were disappearing behind a (29) of smog. American’s remarkable environmental progress in the years (30) is powerful testament to our national will, our technological prowess and our (31) in
A. proved
B. demonstrated
C. manifested
D. verified