Pornchanok Kittiprasert. 1998. An error analysis of business letters written by vocational students. Bangkok:National Institute of Development Administration;
Pornchanok Kittiprasert. (1998) An error analysis of business letters written by vocational students (รายงานผลงานวิจัย). National Institute of Development Administration:Bangkok.
Pornchanok Kittiprasert. An error analysis of business letters written by vocational students. Bangkok:National Institute of Development Administration, 1998.
Pornchanok Kittiprasert. (1998) An error analysis of business letters written by vocational students (รายงานผลงานวิจัย). National Institute of Development Administration:Bangkok.