VanSpanckeren, Kathryn, author
Lembaga Penerangan Amerika Serikat, 2001
Buku Teks
United State Information Agency, 1994
Buku Teks
Abel, Darrel, author
Barron's Educational Series, 1963
Buku Referensi
edited by Hennig Cohen
Basic Book, 1969
Buku Teks
Wachner, Clarence W., author
Macmillan, 1963
Buku Teks