Wonderling, David, author
Open University Press, 2005
Buku Teks
Phelps, Charles E., author
Harper Collins, 1992
Buku Teks
Ashmore, Malcolm
Open University Press, 1990
Buku Teks
Donaldson, Cam, author
Macmillan, 1994
Buku Teks
Cooper, Michael H., author
John Wiley and Sons, 1975
Buku Teks
Clewer, Ann, author
Pearson Education, 1998
Buku Teks