https-web-archive-org-web-20221206104943-http-giasuglory-edu-vn-kien-thuc-kinh-nghiem-khai-niem-ve-cang-bien-tiep-can-tu-unctad-167
https-web-archive-org-web-20221206104943-http-giasuglory-edu-vn-kien-thuc-kinh-nghiem-khai-niem-ve-cang-bien-tiep-can-tu-unctad-167