Wheeler, Margaret
Hart Publishing Company, 1967
Buku Teks
Cottrell, Leonard, author
World Pub., 1964
Buku Teks
edited by Mari Pritchard Parker, Elvio Angeloni
McGraw-Hill, 2013
Buku Teks
Artikel Jurnal
Staeck, John P., author
Mayfield Publishing Company, 2002
Buku Teks