Booth, John A.
Westerview Press, 1993
Buku Teks
Rodriguez, Mario
Prentice-Hall, 1965
Buku Teks
Liss, Sheldon B.
Westview Press, 1991
Buku Teks
Woodward, Ralph Lee
Oxford University Press , 1985
Buku Referensi
Churchill, Anthony
The Johns Hopkins University , 1972
Buku Teks