Biagi, Shirley, author
Cengage Learning, 2015
Buku Teks
Vivian, John, author
Pearson and AB, 2007
Buku Teks
editor, Joseph F. Littell
McDougal, Littel and Company, 1976
Buku Teks
Vivian, John, author
Pearson, 2011
Buku Teks
Blades, Derek W., author
Development Centre of the Organisation for Economic Co-operation and Development, 1974
Buku Teks