Sotyaningrum, Alfra Tien. “Kesalahan-Kesalahan Penulisan Surat”. Efisiensi : Kajian Ilmu Administrasi 12, no. 1 (March 11, 2015). Accessed May 12, 2025. https://journal.uny.ac.id/index.php/efisiensi/article/view/3867.