阅读下面短文，按要求完成短文后的各项任务。

　　Have you ever wondered why birds sing?Maybe you thought that they were just happy．After all, you probably also 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(宣称)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．(2)If a stranger should enter your territory and want to hurt 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．(4)一只鸟也将会做同样的事．But he expects an outsider almost any time, especially at nesting(筑巢)season．So he is screaming(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 spring when they are trying to attract a mate(同伴)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．

任务一：从文中找出一个与establish同义的短语。1．________．

任务二：根据(2)处划线部分的意思来完成下面句子。(每空一词，共2词)

2．You might frighten a stranger away by ________　________ him if he should enter your territory and want to hurt you．

任务三：根据文章，选择最佳选项：

3．What is a bird's“territory”?

A．A place where other families of the same species are welcome．

B．A place where a bird can sing loudly．

C．An area where birds often fight against each other．

D．An area which a bird considers to be its own．

任务四：将(4)处划线句子翻译成英语。4．________．

任务五：用一句话概括本文的中心大意(不超过10个单词)。

5．________．