Sayasemawong, S., and S. Nakjun. “An Improvement of English Listening Ability of Wing 5 Air Force Officers Receiving Instruction with the Guidebooks Combined with Test-based Tutoring”. Ratchaphruek Journal, vol. 12, no. 2, Aug. 2014, pp. 112-8, https://so05.tci-thaijo.org/index.php/Ratchaphruekjournal/article/view/240685.