Cambridge University Press, 2020
eBooks
Bennison, George Mills, author
Routledge, 2013
Buku Teks
Macmillan, 1991
Buku Referensi
Kreutzer, Wolfgang, author
McGraw-Hill, 1986
Buku Teks
edited by Russell O. and Garry D. Mckenzie
Burges Minnepotis, 1974
Buku Teks