As Robert was one day rambling (漫步) about, he happened to cry out, "Ho, ho!" He instantly (立刻) heard coming back from a hill nearby, the same words, "Ho, ho!" In great 1, he said with a loud voice, "Who are you?"  The same words came back, "Who are you?" Robert now cried out 2, "You must be a very foolish boy." "Foolish boy!" came back from the 3 in the same angry way.

    He then went into the bushes (灌木丛) nearby,4 for the boy who, he thought, was mocking (模仿取笑) him. 5, he could find nobody there.

    When he went home, he told his mother that some boy had hidden himself for the 6 of mocking him. "Robert," said his mother, "you are angry with yourself alone. You heard 7 but your own words."

    "Why, mother, 8 can that be?" said Robert.

    "Have you ever heard an echo?" asked his mother.

    "No, what is that?"

    "You know, when you play with your ball, and throw it 9 the side of a house, it bounces (反弹) back to you. If I were outside, by the side of a hill and spoke very loudly, my 10 would be sent back. Then I would hear again the 11 words that I spoke. That, my son, is an echo. When you thought someone was mocking you, it was only 12 own voice bouncing back. If you had spoken kindly, you would have heard a kind 13. Remember this when you are at play with your schoolmates. If any of them are angry, and speak in a loud, angry voice, remember the 14. Then let your words be 15 and kind. Good and kind people will always find themselves among other good and kind people."

若n为正整数，（﹣1）²ⁿ=（　　）

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    However, Marc Van Rijsselberg, a farmer in the Netherlands is now using a____(mix) of sea and fresh water ____(grow) healthy and tasty vegetables.

    He teamed up with scientists from the Free University and divided a farm ____eight negated areas. Separate pipes pumped fresh and sea water, and a computer program created water with eight levels of salinity（含盐度）．

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    He found that potatoes grew better than the other vegetables in the combination of sea and fresh water. Mr. Van Rijsselberg said four kinds of these potatoes would be sent to Pakistan____thousands of hectares of land ____(damage) by salinization (盐化作用) last year.