Hubbard, L. Ron, 1911-1986
Bridge Publications, Inc., 2012
Buku Referensi
Miller, Peter
Little, Brown, 1983
Buku Teks
Griffin, Suzanne
BBC English, 1989
Buku Teks
Feininger, Andreas
Dahara Pertama, 1999
Buku Teks
Aspinall, George
ABC Enterprises , 1984
Buku Teks