阅读理解Whydon'tbirdsgetlostontheirlongflightsfromoneplacetoanother?Scientistshavepuzzledoverthisquestionsformanyyears.Nowtheyarebeginningtofillintheblanks.Notlongagoexperimentssh

题目详情

阅读理解

　　Why don't birds get lost on their long flights from one place to another? Scientists have puzzled over this questions for many years. Now they are beginning to fill in the blanks.

　　Not long ago experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly at 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 had spent its lifetime in a cage and 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. The bird tried to fly in the same direction as that taken by his outdoor cousin. Any change in the position of the stars caused a change in the direction of his flight.

　　Scientists think that doves when flying in daylight use the sun for guidance. But the stars are apparently their principle means of navigation (领航). What do they do when the stars are hidden by clouds? Apparently they find their way by such land marks as mountain ranges coastlines and river courses. But when it's too dark to see these the doves circle helplessly unable to get their bearings (方位).

1．The reason why birds don't get lost on their long flights ________.

[　　]

A．has been known to scientists for years

B．is known by everyone

C．still remains a question

D．has been discovered recently

2．The experiment with the dove indicated that ________.

[　　]

A．a bird having spent its lifetime in a cage has to be thought to navigate

B．a bird that has been caged will not fly long distances

C．some birds seem to follow the stars when they fly at night

D．birds can fly in the same direction as that taken by their cousins