Novey, Donald W
Mosby, 2000
Buku Teks SO
Woodham, Anne
Dorling Kindersley, 1997
Buku Teks SO
Evans, Mark
Hermes House, 2000
Buku Teks SO
Bruce, Debra Fulghum
Macmillan General Reference, 1998
Buku Teks SO
Bruce, Debra Fulghum
Macmillan General Reference, 1998
Buku Teks SO