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   _____   __   __    _____    _    _     ______  
  / ___//  \ \\/ //  / ____|| | || | ||  /_   _// 
  \___ \\   \ ` //  / //---`' | || | ||  `-| |,-  
  /    //    | ||   \ \\___   | \\_/ ||    | ||   
 /____//     |_||    \_____||  \____//     |_||   
`-----`      `-`'     `----`    `---`      `-`'

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發送短信 : Explaining signals and systems with graphics and animations (II)