Decker, William Merrill
University of North Carolina Press, 1990
Buku Teks SO
Swan, Michael
Longmans, 1950
Buku Teks SO
Kramer, Leonie
Sun Books, 1973
Buku Teks SO
Swan, Michael
Longmans Green, 1969
Buku Teks SO
Dupee, F.W.
Doubleday, 1956
Buku Teks SO