Thitirat Thongsa-nga. (1998) A validation of the NC-Test for Mathayom Six students. National Institute of Development Administration:ม.ป.ท.Thitirat Thongsa-nga. 1998. A validation of the NC-Test for Mathayom Six students. ม.ป.ท.:National Institute of Development Administration;Thitirat Thongsa-nga. A validation of the NC-Test for Mathayom Six students. ม.ป.ท.:National Institute of Development Administration, 1998. Print.