https://www.syu.ac.kr/blog/%ed%95%9c%ea%b5%ad%ea%b5%91%ec%9c%a1%ea%b3%bc%ec%a0%95%ed%8f%89%ea%b0%80%ec%9b%90-%ec%a0%95%ea%b7%9c%ec%a7%81-%ec%b1%84%ec%9a%a9-%ea%b3%b5%ea%b3%a0%ec%97%b0%ea%b5%ac%ec%a7%81/%ec%b1%84%ec%9a%a9%ea%b3%b5%ea%b3%a0%ec%97%b0%ea%b5%ac%ec%a7%81-pdf_page_4/