Waller, Jenny
Pustaka Binaman Pressindo, 1994
Buku Referensi
Lawson, Joseph W.R., II
American Management Association;;, 1998
eBooks
Carpendale, Jeremy
Blackwell Publishing, 2006
Buku Teks SO
Thompson, Frank J.
Thomson - Wadsworth, 2003
Buku Teks
Lorayne, Harry
Golden Books Centre SDN. BDN, 1992
Buku Teks