Fromkin, Victoria A.
Holt, Rinehart and Winston, 1981
Buku Teks SO
Hazen, Kirk
Massachusetts : Wiley Blackwell, 2015
Buku Teks SO
Alfonso, Anthony
Sophia University LL Center of Applied Linguistics, 1980
Buku Teks
Argiielles, Alexander
Hollym International Corp, 2000
Buku Teks
Runge, Laura L.
Cambridge University Press, 1997
eBooks