Hess, Peter
Harcourt Brace & Company, 1997
Buku Teks
Meier, Gerald M., author
Oxford University Press, 1984
Buku Teks
Griffin, Keith, author
St. Martin Press, 1989
Buku Teks
Nafziger, E. Wayne, author
Cambridge University Press, 2006
Buku Teks
Todaro, Michael P., author
Longmann, 1978
Buku Teks