Eulau, Heinz, author
Bobbs-Merrill, 1963
Buku Teks
Flavin, Christopher, author
Worldwatch Institute, 1985
Buku Teks
Canterucci, Jim, author
American Management Association;, 2005
eBooks
Chambers, Iain, author
Routledge, 1990
Buku Teks
Shadbolt, Maurice
Hodder and Stoughton, 1972
Buku Teks