Monga, Celestin, author
Lynne Rienner, 1996
Buku Teks
Mair, Lucy, author
The Athlone Press, 1971
Buku Teks
The Work Bank , 1981
Buku Teks
edited by Sharon B. Sticher, Jane L. Partpart
Westview Press, 1988
Buku Teks
Nielsen, Waldemar A., author
Atheneum, 1966
Buku Teks