Rutter, William A., author
s.n., 1973
Buku Teks
Snooks, Graeme Donald
Routledge, 1998
Buku Teks
Collier, John G. (John Greenwood), author
Cambridge University Press, 1994
Buku Teks
Collier, John G. (John Greenwood), author
Cambridge University Press, 1987
Buku Teks
Henn, Harry, Alexander, John R
St.Paul,Minn : West publishing Co, 1983,
Buku Referensi