Edward Kohn
Neb Cliffs Notes, 1994
Buku Teks
Travers, Kenneth J., author
Laidlaw Brothers, 1987
Buku Teks
Brumfiel, Charles Francis, 1914-, author
Addison-Wesley, 1962
Buku Teks
Jurgensen, Ray C., author
Houghton-Miffiln, 1983
Buku Teks
Phillips, Nancymarie, author
Mosby Elsevies, 2007
Buku Teks