Owen, Wilfred, author
Brookings Institution, 1951
Buku Teks
Anthonio akkermans, Peter G. Drake, Bill Mattos, andy Middleton
Hermes House, 2011
Buku Referensi
Waldholz, Michael
Simon & Schuster , 1997
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Miller, Rupert G., author
John Wiley & Sons, 1981
Buku Teks
Bryan Park
Buku Teks