Putri Anzeli Simangunsong, Christina N Saragi, and Kammer Sipayung. “Politeness Strategy Used by President Barack Obama Speech”. Jurnal Onoma: Pendidikan, Bahasa, dan Sastra 10, no. 2 (April 17, 2024): 1542–1548. Accessed July 8, 2025. https://www.e-journal.my.id/onoma/article/view/3502.