Have you ever wondered why birds sing? Maybe you thought that they were just happy. After all, you probably sing when you are happy.

Some scientists believe that birds do sing some of time just because they are happy. However, they sing most of the time for a very different reason. Their singing is a warning to other birds to stay out of their territory.

Do you know what a “territory” is? A territory is an area that an animal, usually the male(man, instead of woman),claims(声明) as its own. Only he and his family are welcome there. No other families of the same kind are welcome. Your yard and house are your territory where only your family and friends are welcome. If a stranger should enter your territory and frighten(恐吓)you, you might shout. Probably this would be enough to frighten him away.

If so, you have actually frightened the stranger away without having to fight him. A bird does the same thing. But he expects an outsider almost any time, especially at nesting(筑巢)season. So he is screaming all the time, whether he can see an outsider or not. This screaming is what we call a bird’s song, and it is usually enough to keep an outsider away.

Birds sing loudest in spring when they are trying to attract a mate and warn others not to enter the territory of theirs.

You can see that birds have a language of their own. Most of it has to do with attracting mates and setting up territories.

51. Some scientists believe that most of the time birds’ singing is actually_____.

A. an expression of happiness             B. a way of warning

C. an expression of anger                 D. a way of greeting

52. It can be inferred from the text that          

A.Bird’s song is not enough to keep an outsider away

B.Birds sing most of the just because they are happy

C.Birds sing loudest when it’s spring only to warn others not to go into their territory

D.Birds sing mostly to attract mates and set up their territories

53. The underlined word “territory” in the second paragraph refers to      

A. a house where families or friends are welcome.

B. a place where a bird shuts at the top of its voice.

C. an area for which birds fight against each other.

D. an area which an animal or bird says it’s own.

54. Why do birds keep on singing at nesting season?

A. They want to invite more friends of his kind

B. Their singing helps frighten outsiders away.

C. They are frightened in their nests in daytime

D. They want to find if there are outsiders around

55. how does the writer explain birds’ singing?

A. by comparing birds with human beings.

B. by reporting experiment results

C. by writing diaries of birds’ daily life

D. by telling birds’interesting stories.

 Have you ever wondered why birds sing? Maybe you thought that they were just happy. After all, you probably sing when you are happy.

Some scientists believe that birds do sing some of time just because they are happy. However, they sing most of the time for a very different reason. Their singing is a warning to other birds to stay out of their territory.

Do you know what a “territory” is? A territory is an area that an animal, usually the male(man, instead of woman),claims(声明) as its own. Only he and his family are welcome there. No other families of the same kind are welcome. Your yard and house are your territory where only your family and friends are welcome. If a stranger should enter your territory and frighten(恐吓)you, you might shout. Probably this would be enough to frighten him away.

If so, you have actually frightened the stranger away without having to fight him. A bird does the same thing. But he expects an outsider almost any time, especially at nesting(筑巢)season. So he is screaming all the time, whether he can see an outsider or not. This screaming is what we call a bird’s song, and it is usually enough to keep an outsider away.

Birds sing loudest in spring when they are trying to attract a mate and warn others not to enter the territory of theirs.

You can see that birds have a language of their own. Most of it has to do with attracting mates and setting up territories.

51. Some scientists believe that most of the time birds’ singing is actually_____.

A. an expression of happiness             B. a way of warning

C. an expression of anger                 D. a way of greeting

52. It can be inferred from the text that          

A.Bird’s song is not enough to keep an outsider away

B.Birds sing most of the just because they are happy

C.Birds sing loudest when it’s spring only to warn others not to go into their territory

D.Birds sing mostly to attract mates and set up their territories

53. The underlined word “territory” in the second paragraph refers to      

A. a house where families or friends are welcome.

B. a place where a bird shuts at the top of its voice.

C. an area for which birds fight against each other.

D. an area which an animal or bird says it’s own.

54. Why do birds keep on singing at nesting season?

A. They want to invite more friends of his kind

B. Their singing helps frighten outsiders away.

C. They are frightened in their nests in daytime

D. They want to find if there are outsiders around

55. how does the writer explain birds’ singing?

A. by comparing birds with human beings.

B. by reporting experiment results

C. by writing diaries of birds’ daily life

D. by telling birds’interesting stories.