Have you ever wondered why birds sing? Maybe you thought that they were just happy. After all ,you probably sing or whistle when you are happy.
Some scientists believe that birds do sing some of the time just because they are happy. However ,they sing most of the time for a very different reason .Their singing is actually 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, claims（声称）as its own .Only he and his family are welcome there .No other families of the same species（物种）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 threaten you, you might shout. Probably this would be enough to frighten him away.
If so, you have actually scared 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 the 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 all their own. Most of it has to do with attracting mates and setting up territories.
56．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
57．What is a bird’s “territory”?
A．A place where families of other species are not accepted.
B．A place where a bird may shout at the top of its voice.
C．An area for which birds fight against each other.
D．An area which a bird considers to be its own.
58．Why do birds keep on singing at nesting season?
A．Because they want to invite more friends.
B．Because their singing helps frighten outsiders away.
C．Because they want to find outsiders around.
D．Because their singing helps get rid of their fears.
59．How does the writer explain birds’ singing?
A．By comparing birds with human beings.
B．By reporting experiment results.
C．By describing birds’ daily life.
D．By telling a bird’s story.
56---59 BDBA
56.解析：这是一道细节题。第二段说“更多情况下，它们的歌唱实际是对其他鸟类置身于它们领域之外的警告”。而A项是some of the time的原因。注意命题中写的是most of the time。
57.解析：这是一道细节推测题。第三段第一行说“领域就是动物，特别是雄性，声称属于自己的区域”。
58.解析：第四段最后一句“这种尖叫就是我们说的鸟的歌唱，它通常足以防范外来者”。
59.解析：第一段就举了“你高兴的时候也会唱歌和吹口哨”的例子；第三、四段也讲了陌生人进入你的地域（家）你也会喊叫的例子。因此作者是用人来和鸟比较。