Downes, John
Barron's Educational Series, 1998
Buku Referensi
Downes, John, author
Barron's Educational Series, 1998
Buku Referensi
Downes, John, author
barron's, 2006
Buku Teks
Hildreth, Sandra S., author
Dearborn Financial Publishing, 1988
Buku Referensi
Jordan, John E.
Harper & Row, Publishers, 1965
Buku Teks