Association of Commonwealth Universities, 1976
Buku Teks
Gee, Wilson, author
D. Appleton-Century Company, 1934
Buku Teks
Walton, Richard E., author
Addison-Wesley, 1969
Buku Teks
Cook, Chris
Macmillan Press , 1984
Buku Teks
Cook, Chris
Macmillan Press , 1989
Buku Teks