Cochran, Thomas C.
Macmillan, 1947
Buku Teks
Johnson, Daniel Milo
Duke University Press, 1981
Buku Teks SO
Tibaijuka, Anna Kajumulo
earthscan, 2009
Buku Teks
Harriott, Stephen
Addison Wesley Longman, 1999
Buku Teks
Dube, Yves
Queen's Printer, 1957
Buku Teks