Natchaya Chalaysap. 1990. Business memos, letters and telex. Bangkok:National Institute of Development Administration;
Natchaya Chalaysap. (1990) Business memos, letters and telex (รายงานผลงานวิจัย). National Institute of Development Administration:Bangkok.
Natchaya Chalaysap. Business memos, letters and telex. Bangkok:National Institute of Development Administration, 1990.
Natchaya Chalaysap. (1990) Business memos, letters and telex (รายงานผลงานวิจัย). National Institute of Development Administration:Bangkok.