Wilson, Graham K., author
Chatham House, 1985
Buku Teks
Lasser, J.K. (Jacob Kay), author
McGraw-Hill, 1960
Buku Teks
Brooks, Ian, author
Prentice-Hall, 1997
Buku Teks
Nickels, William G.,
McGraw Hil , 2016
Buku Teks
Andrews, P.W.S., author
Macmillan, 1949
Buku Teks