George Phillip, 1981
Buku Referensi
edited by B.M. Willet
George Philip and Son, 1981
Buku Referensi
McNally, Rand
Rand McNally & Co, 1963
Buku Referensi
Macmillan, 1990
Buku Teks
[publisher not identified], [date of publication not identified]
Buku Referensi