North, Adrian C.
Oxford, 2008
Buku Teks
editor-in-chief Charles D. Spielberger
Hershey, 2004
Buku Teks
Nicolson, Paula
MacMillan Education, 1986
Buku Teks
Snowman, Jack
Wadsworth and Cengage Learning, 2012
Buku Teks
Blackwell Publishing Limited, 2001
Majalah, Jurnal, Buletin