题目内容：

Why don’t birds get lost on their long flights (飞行) from one place to another? Scientists have studied this puzzle for a long time. Now they’re starting to fill in the blanks(空白).

    Not long ago, experiments showed that birds use the sun to guide them during daylight hours. How do birds fly at night? Tests with artificial stars, which are made by people, have proved that certain night-flying birds are able to follow the stars in their long-distance flights.

They found a bird that spent its lifetime in a cage and never flew under a natural sky. But it was born with the ability to use the stars to look for the direction. This bird’s cage was placed under the sky filled with artificial stars. Any change in the position of the artificial stars caused a change in the direction of the bird’s flight. From the experiment, they found that the bird tried to fly in the same direction as those artificial stars moving under the natural sky.

But the stars are of course birds’ main ways of navigation (航行), when the stars are hidden by clouds, they can still find their way by such landmarks (路标) as river courses, mountain ranges (山脉), coast lines and so on. Because of this ability, people use the dove (鸽子) to send messages in some fields. For example, the doves were used to send messages in both World War I and World War II. During that time, thousands of doves were used to carry important messages in order to save the lives of many thousands of people. So it is also the symbol of peace.

But when it’s too dark to see these things, the doves are not able to find their way. They only circle helplessly and get lost.

根据短文内容选择最佳答案.

1.The underlined word “artificial” in the passage means “________” in Chinese.

A. 艺术的     B. 人造的      C. 永恒的

2.According to the experiments, birds can follow ________ in their flight during the sunny days.

A. the stars    B. the sun     C. the river courses

3.Which picture shows the right direction of the artificial star and birds?

 

4.Which of the following is TRUE according to the passage?

A. The reason why birds don’t get lost on long flights has been known to scientists for many years.

B. The stars are of course birds’ only ways of navigation.

C. In the darkness, doves can’t find their way.

5. What is this passage mainly about?

A. Birds can fly a long distance. 

B. The dove is the symbol of peace.

C. How the birds find their ways.