题目内容
（请给出正确答案）
Pigeons have a natural instinct for ______.
A．going back home
B．growing fast
C．flying at a high speed
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A.A know what they want to achiev
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D.D can be driven by national prid
Science seems to be getting closer to answering a very old mystery (奥秘). Homing pigeons (信鸽) can be taken hundreds of miles from their homes. When they are let to go to fly again, they find their way home. Because of this special ability to find home, pigeons have been used as messengers for hundreds of years.
Today people even breed homing pigeons for racing as a sport. The birds are shipped to some chosen place a few hundred miles away. Then all of them are let to go together. The winner is the bird that gets home first. A good racer can make it home from 500 miles away in a single day.
The mystery of the homing pigeon is how it tells direction and how it finds home.
The first part seems to be pretty well answered, and we know of two ways that pigeons tell directions. First, they use the sun. Experiments show that homing pigeons can tell directions by the sun. What happens when the sky is darkly overcast by clouds and no one can see where the sun is？ Then the pigeons still find their way home.
Naturally, people have wondered whether pigeons might have a built-in compass—something that would tell them about the direction of the earth’s magnetic (磁的) field. Many different kinds of experiments were done. Here’s what the scientists decided after they had made experiments many times. When pigeons can see the sun, they use it as their main means(手段)of direction-finding. When they cannot see the sun, they use some special way to sense direction from the earth’s magnetic field.
But how do pigeons know which direction is toward home？ What do they use that we would call a map？ These are other questions to be answered.
Pigeons have been used as messengers because ______.
A．they have a built-in compass
B．they can cover 500 miles in a single day
C．they have special ability to tell directions
D．they can find their way home
Pigeons have been known to fly as fast as ______.
A．75 mph
B．50 mph
C．110 mph
D．62 mph
【T6】
LEARN TO ON OR NOT A. WHETHER WE LIKE IT【T1】______
B. HAVE TO【T2】______ ACCEPT
C. THAT EXISTS【T3】______ PLANET EARTH THE FILM SHOWS HOW WONDERFULLY GENTLE AND CARING ELEPHANTS ARE, AND JUST HOW INTELLIGENT AND "HUMAN" THEY ARE AS WELL. PEOPLE【T4】______ THAT WE HUMANS ARE, IN FACT, ANIMALS.【T5】______ , WE ARE STILL PART OF THE WHOL
E. EVERY SPECIES【T6】______ HAS A ROLE TO PLAY. THE ROLE OF HUMANS HAS, ON THE WHOLE, BEEN DESTRUCTIV
E. HUMANS NEED TO HAVE MORE RESPECT FOR NATUR
E.
【T1】
LEARN TO ON OR NOT A. WHETHER WE LIKE IT【T1】______
B. HAVE TO【T2】______ ACCEPT
C. THAT EXISTS【T3】______ PLANET EARTH THE FILM SHOWS HOW WONDERFULLY GENTLE AND CARING ELEPHANTS ARE, AND JUST HOW INTELLIGENT AND "HUMAN" THEY ARE AS WELL. PEOPLE【T4】______ THAT WE HUMANS ARE, IN FACT, ANIMALS.【T5】______ , WE ARE STILL PART OF THE WHOL
E. EVERY SPECIES【T6】______ HAS A ROLE TO PLAY. THE ROLE OF HUMANS HAS, ON THE WHOLE, BEEN DESTRUCTIV
E. HUMANS NEED TO HAVE MORE RESPECT FOR NATUR
E.
【T5】
LEARN TO ON OR NOT A. WHETHER WE LIKE IT【T1】______
B. HAVE TO【T2】______ ACCEPT
C. THAT EXISTS【T3】______ PLANET EARTH THE FILM SHOWS HOW WONDERFULLY GENTLE AND CARING ELEPHANTS ARE, AND JUST HOW INTELLIGENT AND "HUMAN" THEY ARE AS WELL. PEOPLE【T4】______ THAT WE HUMANS ARE, IN FACT, ANIMALS.【T5】______ , WE ARE STILL PART OF THE WHOL
E. EVERY SPECIES【T6】______ HAS A ROLE TO PLAY. THE ROLE OF HUMANS HAS, ON THE WHOLE, BEEN DESTRUCTIV
E. HUMANS NEED TO HAVE MORE RESPECT FOR NATUR
E.
【T3】
LEARN TO ON OR NOT A. WHETHER WE LIKE IT【T1】______
B. HAVE TO【T2】______ ACCEPT
C. THAT EXISTS【T3】______ PLANET EARTH THE FILM SHOWS HOW WONDERFULLY GENTLE AND CARING ELEPHANTS ARE, AND JUST HOW INTELLIGENT AND "HUMAN" THEY ARE AS WELL. PEOPLE【T4】______ THAT WE HUMANS ARE, IN FACT, ANIMALS.【T5】______ , WE ARE STILL PART OF THE WHOL
E. EVERY SPECIES【T6】______ HAS A ROLE TO PLAY. THE ROLE OF HUMANS HAS, ON THE WHOLE, BEEN DESTRUCTIV
E. HUMANS NEED TO HAVE MORE RESPECT FOR NATUR
E.
【T5】
A.WHETHER WE LIKE IT【T1】______
B.HAVE TO【T2】______ACCEPT
C.THAT EXISTS【T3】______PLANET EARTH THE FILM SHOWS HOW WONDERFULLY GENTLE AND CARING ELEPHANTS ARE, AND JUST HOW INTELLIGENT AND "HUMAN" THEY ARE AS WELL. PEOPLE【T4】______THAT WE HUMANS ARE, IN FACT, ANIMALS.【T5】______,WE ARE STILL PART OF THE WHOL
E. EVERY SPECIES【T6】______HAS A ROLE TO PLAY. THE ROLE OF HUMANS HAS,ON THE WHOLE, BEEN DESTRUCTIV
E. HUMANS NEED TO HAVE MORE RESPECT FOR NATUR
E.
