Williams, Basil, author
Oxford University, 1945
Buku Klasik
editors and contributors, Joseph J. Norton, Thomas L. Bloodworth ; editorial coordinator, Terry K. Pennington
Martinus Nijhoff Publishers, 1995
Buku Teks
National Geographic Society, 1955
Buku Teks
Khanna, Ro, 1976-, author
McGraw-Hill, 2012
Buku Teks
Morris, Michael A, author
Palgrave Macmillan, 2016
Buku Teks