... 2002, 2004; Duong Bach Nhat, 2008; Nguyen Van Do, 1996, 1999; Nguyen Duc Hoat, 1995; Vu Thi Thanh Huong, 1997, 2002; Pham Thi Hong Nhung, 2007ab) with reference to Vietnamese are introduced ... be investigated with a focus on another socio-cultural variable like the social distance (Pham Anh Toan, 2005, in expressing gratitude) or on some non verbal factors (i.e., paralinguistic factors...