Greenlees, Ian
Longman Group, 1971
Buku Teks
Riddle, Douglas F.
PWS Publishing Co., 1992
Buku Teks
McQuaig, Douglas J.
Houghton Mifflin, 1989
Buku Teks
Pike, Dauglas
Cambridge at the University Press, 1966
Buku Teks
Cassell, Douglas A.
Reston Publishing, 1983
Buku Teks