Williams, Venus, author
Amistad, 2010
Buku Teks
Ziglar, Zig, author
Heinemann Asia, 1995
Buku Teks
Ray, James Arthur, author
Gramedia Pustaka Utama, 2009
Buku Teks
O`Neil, John R., author
McGraw-Hill, 1995
Buku Teks
Haig, Matt
Elex Media Komputindo,
Buku Teks