Duckworth, Angela, author
Gramedia Pustaka Utama, 2018
Buku Teks
Tracy, Brian, author
American Management Association, 2002
eBooks
Poissant, Charles-Albert
Pustaka Tangga, 1993
Buku Teks
Robbins, Anthony
A Freeside Book, 1991
Buku Teks
Maxwell, John C., author
Harvest Publication House, 1997
Buku Teks