Appleby, Pauline
Glorier International, 2001
Buku Referensi
Juniper, Dean
Glorier International, 2001
Buku Referensi
Kneeland, Steve
Glorier International, 2001
Buku Referensi
Record, Matthew
Glorier International, 1999
Buku Referensi
Dauten, Carl Anton, 1913-
Prentice-Hall, 1948
Buku Teks