Scotland, 1999
Buku Referensi
Tiger Books International, 1994
Buku Referensi
Katzner, Kenneth, author
John Wiley & Sons, 1994
Buku Referensi
Eckersley, C. E. (Charles Ewart), 1892-1967, author
Longmans, Green and Co., 1953
Buku Referensi
Oxford university press , 1992
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