Churchill, Gilbert A., author
Thomson, 2005
Buku Teks
[publisher not identified], [date of publication no identified]
Buku Teks
[publisher not identified], [date of publication no identified]
Buku Teks
Hillway, Tyrus, author
Houghton Miffiln, 1964
Buku Teks
Cooper, Donald R., author
McGraw-Hill/Irwin, 2006
Buku Teks