Cook, Vivian
ARNOLD, 2001
Buku Teks
Ellis, Rob
Blackwell, 1990
Buku Teks
Leaver, Betty Lou
Cambridge Press , 2005
Buku Teks
edited by Jessica Williams and Bill Van Patten
NY : Routledge, 2015
Buku Teks
Richards, Jack C.
Cambridge University Press, 2015
Buku Teks