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     Mark Twain was born in a small town of Horrid. When he is only twelve years old , his father died .

Late he became a river boat pilot . Mark Twain was her pen name .During the American Civil War he

worked as a reporter and write a lot of stories. Gradually he made his mark and his work were popular .

He became one of the best known writer of the 19th century in the U.S.A . In his life Mark Twain wrote

the number of stories and novels , of them  "Adventure of Tom Sawyer" is the most famous one . His

writings have  translated into many other languages ,and they are deeply loved by the readers all over in

the world .        

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退快冷装置时汽机第一级金属温度及中压持环金属温度均需低于（）。