Stubbs, Amanda, author
Thomas Telford, 1998
Buku Teks
Schwartz, Mortimer D., author
Gale Research, 1977
Buku Teks
Rodgers, William H., author
St. Paul Minn, 1977
Buku Teks
Rodgers, William H., author
West Publishing, 1994
Buku Teks
Kubasek, Nancy K., author
Pearson - Prentice Hall, 2005
Buku Teks