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German ornithologists proved that birds have a______guiding their navigatory behavior. though some biologists argued that it was impossible for birds to sense the weak magnetic force of the Earth.

A.
【参考答案】

magnetic compass
magnetic compass

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Wildlife refuges mainly serve as havens for millions of ducks, geese and other migratory birds. And this is what most people come to seE.Much of the fun is in knowing and distinguishing the many kinds that are present in great variety. The activities and antics of the bird world are fascinating to anyone taking the time to observe up closE.A camera, likewise, will record some of the unusual sights that will be seen.
Most of the areas are staffed by biologists--individuals who have a great interest in the out doors. They are all enthusiastic naturalists who can help a person to a richer enjoyment of the world of naturE.A stop at the refuge headquarters will yield ideas on what to see and where, as well as helpful literaturE.A few refuges have visitor centers where displays tell the story of the refuge and where there are movies or color slide shows of the area and its wildlifE.
Hunting on a refuge seems inconsistent with its purpose of protecting and saving. However, big game, if allowed to increase to an excessive degree, can be their own worst enemy. They overbrowse their rangE.Then starvation ruins the herD.But even before nature balances animals to food supply, the destruction of trees and shrubs removes food and cover essential to many smaller animals as well. It' s good management of the game, and to the sportsman' s benefit, to crop big game judiciously.
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