Covey, Stephen R., author
Simon & Schuster, 2013
Buku Teks
Covey, Stephen R., author
Simon & Schuster , 1990
Buku Teks
Tracy, Brian, author
John Wiley & Sons, 2003
Buku Teks
Oech, Roger Von, author
Bhuana Ilmu Populer, 2008
Buku Teks
Bryan Lo`s, author
Awesome Books Publishing SDN BHN, 2002
Buku Teks