Ronald Creighton-Jobe, consultant
Hermes House, 2017
Buku Referensi
Kerrigan, Michael
Leicestershire Southwater, 2011
Buku Referensi
Hey, Barbara
New Holland, 1994
Buku Teks
Kenny, Anthony, author
Blackwell Publishing, 2007
Buku Teks
Gebhard, Jerry G., author
Cambridge University Press, 1999
Buku Teks