Lye, Keith
The Royal Geographical Society, 2000
Buku Referensi
Kidron, Michael
Simon & Schuster, 1984
Buku Teks SO
Debenham, Frank
Reader's Digest Association, 1979
Buku Referensi
C. S. Hammond and Company
C.S. Hammond & Co., [date of publication not identified]
Buku Teks SO
C.S. Hammond , 1961
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