（Par1, Passage 1）
Why don’t birds get lost on their long flights from one place to another

The reasons why birds don't get lost on long flights ______.

A．have been known to scientists for years

B．have only recently been discovered

C．are known by everyone

D．will probably remain a mystery

The reasons why birds don't get lost on long flights______.

A．have been known to scientists for years

B．have only recently been discovered

C．are known by everyone

D．will probably remain a mystery

Task 1

Directions: After reading the following passage, you will find 5 questions or unfinished statements, numbered 36 through 40. For each question or statement there are 4 choices marked A, B, C, and D. You should make the correct choice.

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

Not long ago, experiments showed that birds rely on the sun to guide th

The reason why birds don't get lost on long flights ______.

A．have been known to scientists for years

B．have only recently been discovered

C．are known by everyone

D．will probably remain a mystery

Task 2

Directions: This task is the same as Task 1. The 5 questions or unfinished statements are numbered 41 through 45.

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

Not long ago, experiments showed that birds depend on the sun to guide

The reason why birds don't get lost on long flight ______.

A．has been discovered recently

B．is known by everybody

C．still remains a mystery

D．has been known to scientists for years

A．have been known to scientists for years

B．have only recently been discovered

C．are known by everyone

D．will probably remain a mystery

听力原文： Why don't birds get lost on their long flights from one place to another？ Scientists have puzzled over this question 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 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 had spent his 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. 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.

But the stars are apparently their principal means of navigation. When the stars are hidden by clouds, they apparently 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．has been known to scientists for years

B．has only recently been discovered

C．is known by everyone

D．will probably remain a mystery

Why don't we get rid of these books since we don't use them ______．

既然我们都不用这些书了，为何不丢掉它们？

Experiments showed that ______.

A．birds are likely to get lost if there aren't man-made stars.

B．day-flying birds depend on the sun while night-flying birds depend on the stars

C．birds depend on the sun to guide them

D．birds depend on the stars to guide them