Her Majesty's Stationery Office, 1987
Buku Teks
edited by Maria Slowey, David Watson
Open University Press, 2003
Buku Teks
Smith, Huston, author
Harper & Brothers, 1955
Buku Teks
Mayhew, Lewis B., author
Jossey-Bass, 1973
Buku Teks
Brubacher, John S.
McGraw-Hill, 1965
Buku Teks