Rosenwasser, David, author
Harcourt Brace & Company, 1997
Buku Teks
Moore, Robert Hamilton, author
Holt, Rinehart and Winston, 1959
Buku Teks
Bruington, Pat, author
Charles E. Merrill, 1984
Buku Teks
Yates, Edward D., author
Contemporary Publishing Company, 1981
Buku Teks
Department of External Affairs, 1963
Buku Teks