[单项选择]Prudent investors learned long ago that putting your eggs into lots of baskets reduces risk. Conservationists have now hit on a similar idea: a population of endangered animals will have a better chance of survival if it is divided into interconnected groups. The prospects of the species will be better because the chance that all the constituent subpopulations will die out at the same time is low. And, in the long term, it matters little if one or two groups do disappear, because immigrants from better-faring patches will eventually re-establish the species’ old haunts.
One endangered species divided in just this way is the world’s rarest carnivore, the Ethiopian wolf, which lives high in the meadows of the Bale Mountains. Just 350 exist in three pockets of meadow connected by narrow’ valleys in the Bale Mountains National Park, with a further 150 outside this area.
Two of the main threats to the Ethiopian wolf come from diseases carried by domestic dogs. One of these, rabies
A. is facing the risk of extinction as the rarest carnivore.
B. is separated into three groups to achieve survival.
C. lives in narrow valleys in the Bale Mountains.
D. has altogether 350 alive in the world.

Prudent investors learned long ago that putting your eggs into lots of baskets reduces risk. Conservationists have now hit on a similar idea: a population of endangered animals will have a better chance of survival if it is divided into interconnected groups. The prospects of the species will be better because the chance that all the constituent subpopulations will die out at the same time is low. And, in the long term, it matters little if one or two groups do disappear, because immigrants from better-faring patches will eventually re-establish the species’ old haunts.
One endangered species divided in just this way is the world’s rarest carnivore, the Ethiopian wolf, which lives high in the meadows of the Bale Mountains. Just 350 exist in three pockets of meadow connected by narrow’ valleys in the Bale Mountains National Park, with a further 150 outside this area.
Two of the main threats to the Ethiopian wolf come from diseases carried by domes
A. conservationists got inspirations from it.
B. endangered animals can be protected in a similar way.
C. the prospects of some species depend on conservation.
D. the subpopulations will die without being put into different groups.

Long long ago mankind began to use tools. Throughout the world, you can still find the tools which were used over two million years ago. People made such tools by hitting one stone (36) another. By this means, they got pieces from one of the stones. These pieces of stone were always (37) on one side. People utilized them to (38) skin and meat from some animals that were dead, (39) to make other tools from wood. Mankind needed (40) use tools since, unlike other meat-eating (41) , say lions, they did not have sharp teeth. Tools greatly helped people obtain food more (42) .
Tools helped (43) human intelligence as well when human worked with them. The human brain became bigger gradually, and human beings began to invent a growing number of tools. The stone piece was one of the (44) tools that were used by people, and maybe it was (45) . Some scientists hold it was the key (46) huma
A. from 
B. to 
C. for 
D. in