United States Information Agency, 1987
Buku Teks
Board of Trusless, 1960
Buku Referensi
Walker, Edward Everett, 1900-1974, author
Charles Scribner's Sons, 1943
Buku Teks
Kamerman, Sheila B., author
Temple University Press, 1976
Buku Teks
Williams, T. Harry, author
Alfred A. Knopf, 1963
Buku Teks