A俄国作曲家柴科夫斯基
B波兰作曲家里姆斯基—柯萨科夫
C波兰作曲家柴科夫斯基
D俄国作曲家里姆斯基—柯萨科夫
The ability of birds to return to a familiar place from any distance is a remarkable feat of nature. For centuries people have taken advantage of this ability in homing pigeons by using them to take messages from distant points back to familiar sites. Homing pigeons are domesticated non-migratory birds with an instinct to return to their lofts (nesting sites) that is improved with training and by selective breeding. Training is started at short distances from the nesting site; over time, this distance is gradually increased to hundreds of miles from its loft at a completely unfamiliar location and it can fly in the direction of home within a minute or two of its release. How does this extraordinary behavior. work?
Understanding homing behavior. is one of the greatest challenges to ornithologists (鸟类学家). Fortunately, because they are able to carefully control the conditions under which the pigeons are released, researchers have been able to learn a great deal about how the birds navigate their way home.
Although homing ability has been fostered in pigeons by careful breeding and selecting of stock, it appears that training is not always necessary: Many species of wild birds perform. similarly remarkable feats. One such bird is the migratory Manx Shearwater (剪嘴鸥). Built like tiny albatrosses, these seabirds spend most of their lives skimming over the ocean surface far from the sight of land. They come ashore only to nest in burrows, which they dig in the ground on offshore islands in order to be safe from predators. The ease of locating and observing their nests make shearwaters ideal subjects for homing experiments.
Great Bird Navigators
Many migratory birds are remarkably faithful to previous nesting and overwintering places. Though a bird might be able to come close to these sites merely by flying in a general direction during the course of migration, at some point more sophisticated navigating techniques must take over to guide the bird to its precise destination.
Many animals are able to find their way home. One way of doing this is to directly sense the goal—to see, hear, or smell it. Another way is to memorize the details of the outward journey and then reverse the route based on an integration of that information. Birds, however, apparently rely on a completely different process to find their way. To explain bird navigation, we have what is known as the "map-and-compass" theory.
The compass component of this theory gives direction--north, south, east, west; the map component tells the bird where it is, or gives locality. Scientists have learned a great deal more about the compass component than they have about mapping. They know that birds have several means of determining compass directions, but unfortunately, they still have no satisfactory explanation for how birds use biological "maps" to guide them to a precise location from an unfamiliar starting point.
Bird Sun Navigators
Some observations indicate that birds might use the sun as, a visual cue to determine compass directions. Starlings (八哥), for example, seem able to negotiate the proper direction only if they have a view of the clear sky and sun; cloud cover seems to induce confusion. In an experiment in which the sun's apparent position was changed with mirrors attached to an orientation cage containing starlings, observers noted that the direction of the starlings' hopping, which earlier had been correlated to the direction that chose to migrate, was shifted accordingly.
Even birds that migrate exclusively at night pay considerable attention to the sun. At first this may seem odd because, after all, the sun is not visible to the nocturnal (夜间活动的) birds when they are flying. On the other hand, it is a predominant feature in the sky at a time of day (dusk)when birds may well be making decisions about w
A．Y
B．N
C．NG
根据一种心理学理论，人要想快乐，就必须与其他人保持亲密关系。然而世界上最伟大的作曲家们通常都是孤独地度过他们的大部分时光，并且没有和别人保持亲密关系。因此，这种心理学理论必定是错误的。上述结论假定了：
A．世界上最伟大的作曲家们会避免与人保持亲密关系。
B．那些与别人有亲密关系的人在生活中很少有孤独的时候。
C．世界上最伟大的作曲家们是快乐的。
D．不太出名的作曲家通常与别人有亲密关系。
