求翻译：In the Song Dynasty (960-1279), a man named Bi Sheng carved individual characters on identical pieces of fine clay. Each piece of movable type had on it one Chinese character which was carved in relief on a small block of moistened clay. After the block had been hardened by fire, the type became hard and durable and could be used wherever required. The pieces of movable type could be glued to an iron plate and easily detached from the plate. Each piece of character could be assembled to print a page and then broken up and redistributed as needed. When the printing was finished, the pieces were put away for future use.是什么意思？

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