Taviz Tatnormjit และ Therdchai Choibamroong. (2015) The development of procedure to reinforce youth tourism world heritage in historic town of Sukhothai and associated historic towns. National Institute of Development Administration:ม.ป.ท.Taviz Tatnormjit และ Therdchai Choibamroong. 2015. The development of procedure to reinforce youth tourism world heritage in historic town of Sukhothai and associated historic towns. ม.ป.ท.:National Institute of Development Administration;Taviz Tatnormjit และ Therdchai Choibamroong. The development of procedure to reinforce youth tourism world heritage in historic town of Sukhothai and associated historic towns. ม.ป.ท.:National Institute of Development Administration, 2015. Print.