[单项选择]

Despite decades of scientific research, no one yet knows how much damage human activity is doing to the environment. Humans are thought to be responsible for a whole host of environmental problems, ranging from global warning to ozone depletion. What is not in doubt, however, is the devastating effect humans are having on the animal and plant life of the planet.
Currently, an estimated 50,000 species become extinct every year. If this carries on, the impact on all living creatures is likely to be profound, says Dr. Nick Middleton, a geographer at Oxford University. " All species depend in some way on each other to survive. And the danger is that, if you remove one species from this very complex web of interrelationships, you have very little idea about the knock-on effects of other extinctions. "
Complicating matters is the fact that there are no obvious solutions to the problem. Unlike global warning and ozone depletion—which, if the political wil
A. Global warming and ozone depletion
B. Species extinction and corruption
C. Sustainable management
D. A gigantic experiment we’re conducting with Earth

Despite decades of scientific research, no one yet knows how much damage human activity is doing to the environment. Humans are thought to be responsible for a whole host of environmental problems, ranging from global warning to ozone depletion. What is not in doubt, however, is the devastating effect humans are having on the animal and plant life of the planet.
Currently, an estimated 50,000 species become extinct every year. If this carries on, the impact on all living creatures is likely to be profound, says Dr. Nick Middleton, a geographer at Oxford University. " All species depend in some way on each other to survive. And the danger is that, if you remove one species from this very complex web of interrelationships, you have very little idea about the knock-on effects of other extinctions. "
Complicating matters is the fact that there are no obvious solutions to the problem. Unlike global warning and ozone depletion—which, if the political wil
A. Reduction of the impact of species extinction on others
B. Sustainable management of the world’s tropical forests
C. Encouragement of political will to reduce gas emission
D. No effective way has been found yet