Dunham, Barrows, author
Little, Brown and Company, 1947
Buku Teks
Gray, J.A. Muir, author
Oxford University Press, 1979
Buku Teks
Murray, Raymond W., author
Bruce Publishing, 1943
Buku Teks
Clark, Wilfrid E. Le Gros, author
Holt, Rinehart and Winston, 1967
Buku Teks
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