Natthaphon Santhi และผู้แต่งคนอื่นๆ. (2012) A study of e-mail writing ability of Chiangrai Rajabhat University 4th year tourism industry students. Chulalongkorn University:ม.ป.ท.Natthaphon Santhi และผู้แต่งคนอื่นๆ. 2012. A study of e-mail writing ability of Chiangrai Rajabhat University 4th year tourism industry students. ม.ป.ท.:Chulalongkorn University;Natthaphon Santhi และผู้แต่งคนอื่นๆ. A study of e-mail writing ability of Chiangrai Rajabhat University 4th year tourism industry students. ม.ป.ท.:Chulalongkorn University, 2012. Print.