https://itmanual.net/%ed%8c%8c%ec%9b%8c%ed%8f%ac%ec%9d%b8%ed%8a%b8-%eb%ac%b4%eb%a3%8c%ed%8f%b0%ed%8a%b8-%ec%a0%81%ec%9a%a9-%eb%b0%8f-ppt-%ed%8f%b0%ed%8a%b8-%ec%a0%80%ec%9e%a5-%eb%b0%a9%eb%b2%95/