Trang, Tran Thi Thuy. β€œAn Investigation into Linguistic Problems in Writing English Business Complaint Letters. A Case Study at Universal Petroleum Viet Nam Joint Stock Company.” International Journal of English Literature and Social Sciences, vol. 10, no. 2, 2025, pp. 113–19. Crossref, https://doi.org/10.22161/ijels.102.20.