Laquian, Aprodicio A., author
University of Philippines, 1966
Buku Teks
Katz, Saul M., author
University of Pittsburgh, 1965
Buku Teks
MacDonald, Austin F., author
Thomas Y. Crowell, 1949
Buku Teks
MacDonald, Austin F., author
Thomas Y. Crowell , 1951
Buku Teks
Westview Press, 1994
Buku Teks