Garrison, Sharon Hatten
Quorum Books, 1988
Buku Teks
Hanke, John E., author
Prentice Halls, 2001
Buku Teks
Hanke, Jonh E., author
Pearson Prentice Hall, 2005
Buku Teks
Bratt, Elmer C., author
McGraw-Hill, 1958
Buku Teks
Robinson, Colin, author
Nelson, 1971
Buku Teks