Lovering, W.F.
Longmans, 1966
Buku Teks
Burgess, W. Randolph
Harper & Brothers , 1946
Buku Teks
Thomas, F.W.
University of Calcuta, 1942
Buku Teks SO
edited by Peter Newman, Murray Milgate and John Eatwell
Macmillan, 1992
Buku Referensi
Burton, Ian
The Guilford Press, 1993
Buku Teks