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如图,设集合A,B为全集U的两个子集,则A∪B=____

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{1,2,3,4,5}

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    People have used pigeons to carry messages to one another for hundreds of years. In fact, pigeons were a common way to send messages right up through Would War II.

    In 1815, English troops were fighting Napoleon's forces in France, and the English were believed to be losing. A financial panic swept over London. Government bonds(债券)were offered at low prices. Few people noticed that Nathan Rothschild, an English banker, was snapping up these bonds when everyone else was trying to sell them. A few days later, London learned the truth: the Duke of Wellington had defeated Napoleon at the battle of Waterloo. The value of the bonds soared(暴涨), and Rothschild became wealthy…all because his pigeons had brought him news of the victory before anyone else knew of it.

    Carrier pigeons were used by countries in both World War I and World War II. Not only were the birds often the fastest, most reliable way to send messages, they could also be used to reach soldiers far behind enemy lines, where radios and field telephone lines were useless. Since they could easily be released from airplanes or ships, every branch of the armed services used the birds.

    Carrying messages could be a dangerous job. Some pigeons performed with such bravery that they became famous and were even awarded medals. The most famous pigeon of all may have been Cher Ami. Stationed in France during World War I, he carried twelve important messages for American forces. On his last mission, though wounded, he carried a message that saved the lives of 194 American soldiers. For his amazing service, he was awarded the French “Croix de Guerre.”

    Today, modern communication methods can carry information from one place to another hundreds of times faster than a pigeon could do it. However, few people would argue with the fact that carrier pigeons — especially those that served in the military — have earned their place in history.