閱讀下面短文，按要求完成短文后的各項任務(wù)。

　　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(宣稱)as its own．Only he and his family are welcome there．No other families of the same species(物種)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)一只鳥也將會做同樣的事．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．

任務(wù)一：從文中找出一個與establish同義的短語。1．________．

任務(wù)二：根據(jù)(2)處劃線部分的意思來完成下面句子。(每空一詞，共2詞)

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

任務(wù)三：根據(jù)文章，選擇最佳選項：

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．

任務(wù)四：將(4)處劃線句子翻譯成英語。4．________．

任務(wù)五：用一句話概括本文的中心大意(不超過10個單詞)。

5．________．