Narongrit Sopa และผู้แต่งคนอื่นๆ. (2010) Foreign Language Competency Development of Tour Guides in Geology and Fossils in the Northeast of Thailand. <i>Rjabhat Maha Sarakham University Journal Humanities and Social Sciences</i>, <i>4</i>(3), 33-35.Narongrit Sopa และผู้แต่งคนอื่นๆ. "Foreign Language Competency Development of Tour Guides in Geology and Fossils in the Northeast of Thailand". Rjabhat Maha Sarakham University Journal Humanities and Social Sciences 4 (2010):33-35.Narongrit Sopa และผู้แต่งคนอื่นๆ. Foreign Language Competency Development of Tour Guides in Geology and Fossils in the Northeast of Thailand. Rjabhat Maha Sarakham University:ม.ป.ท. 2010.