https://blog.gongquiz.com/2022/01/15/%eb%94%94%ec%95%84%eb%b8%94%eb%a1%9c2-%ec%8b%b1%ea%b8%80%ed%94%8c%eb%9f%ac%ea%b8%b0-d2nt-%eb%8f%8c%eb%a6%ac%ea%b8%b0-%e3%82%93/