Have you ever wondered why birds sing? Maybe you thought that they were just happyAfter a

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 as its own ．Only he and his family are welcome there ．No other families of the same species 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's screaming （高声尖叫） 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 of their own．Most of it has something to do with attracting mates and setting up territories．
【小题1】Some scientists believe that most of the time birds' singing is actuallyA．an expression of happinessB．a way of warningC．an expression of angerD．a language of their own【小题2】What is a bird's territory?A．A place where a bird may shout at the top of its voice．B．A place where other bird families are not accepted．C．An area for which birds fight against each other．D．An area which a bird considers to be its own【小题3】Why do birds keep on singing at nesting season?A．Because their singing helps frighten outsiders away．B．Because their singing helps get rid of their fears．C．Because they want to find outsiders around．D．Because they want to invite more bird friends．【小题4】How does the writer explain birds' singing?A．By comparing birds with human beings．B．By reporting experimental results．C．By describing birds'daily life．D．By telling a bird's story．B

(答案→)B 解析：本文通过与人类的对比，讲述了鸟的叫声存在着不同的含义。【小题1】B考查细节题。根据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．可知答案为B。【小题2】D考查细节题。根据A territory is an area that an animal, usually the male, claims as its own.可知答案为D。【小题3】A根据倒数第二段可知，在筑巢期间它的叫声其实是在吓走外面的鸟。【小题4】A通读全文我们不难看出，作者不断地把人类和鸟进行对比。

就是这个解释