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西德发明了一种专门供记载保密内容的“保密文件纸”.这种文件纸含有光致变色物质,不能用复印机复制,也不能使用闪光灯拍摄.由于光致变物质的作用,当受到一
West Germany invented a special “confidential document paper” that contains the confidential information, which contains photochromic substances that can not be copied by a photocopier and can not be taken with a flash. Due to the action of the photochromic substance,