edited by Peter Childs, Mike Storry
Routledge, 1999
Buku Referensi
edited by Kwesi Owusu
Routledge , 2000
Buku Teks
Smith, Leslie
Macmillan, 1989
Buku Teks
Vandersteen, Willy
Standaard, 2012
Buku Teks
Hough, Michael
Research Office Research and Statistics Directorate, 1998
Buku Teks