A.白居易的诗句:日出江花红胜火,春来江水绿如蓝
B.苏东坡的诗句:水光激滟晴方好,山色空蒙雨亦奇
C.林升的诗句:山外青山楼外楼,西湖歌舞几时休
D.杜牧的诗句:南朝四百八十寺,多少楼台烟雨中
Not long age, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly by night? Tests with artificial stars have proved that certain night - flying birds are able to follow the stars in their long - distance flights.
A dove (鸽子) had spent its lifetime in a cage and had never flown under a natural sky. Yet it showed an inborn ability to use the stars for guidance. The bird's cage was placed under an artificial star - filled sky. (76) The bird tried to fly in the same direction as that taken by his outdoor cousins. Any change in the position of the artificial stars caused a change in the direction of his flight.
(77) But the stars are apparently their principal means of navigation (航行) only. When the stars are hidden by clouds, they seemingly find their way by such landmarks as mountain ranges, coast lines, and river courses. But when it's too dark to see these, the doves circle helplessly, unable to find their way.
The reason why birds don't get lost on long flights ______.
A.have been known to scientists for many years
B.have only recently been discovered
C.are known by us
D.will probably remain a mystery
A.由于大部分记忆都衰退,因此早期的经历不易记起
B.主要表现为健忘,电话、地址常遗忘
C.由于注意力减退,因此短时记忆差
D.与感官器官功能衰退有关