Hedgecoe, John, author
Ebury, 1992
Buku Referensi
Hubbard, L. Ron, 1911-1986, author
Bridge Publications, Inc., 2012
Buku Referensi
Miller, Peter
Little, Brown and Company, 1983
Buku Teks
Griffin, Suzanne
BBC English, 1989
Buku Teks
Freininger, Andreas
Dahara Pertama, 1999
Buku Teks