Bakke, Edward Wight
Charlew E. Merrill Books, 1963
Buku Teks
Artikel Jurnal
Jackson, Grdon E.
Prentice-Hall, 1993
Buku Referensi
edited by John F. Burton ... [and others]
Holt, Rinehart and Winston, 1971
Buku Teks
edited by Margaret S. Gordon
McGraw-Hill, 1974
Buku Teks