Artikel Jurnal
Ellig, Jerome, 1962-author
Fla. : CRC, 2012
Buku Teks
Walker, Edward Everett, 1900-1974, author
Charles Scribner's Sons, 1943
Buku Teks
Boyd, Anne Morris, author
H.W. Wilson, 1949
Buku Teks
edited by Max F. Millikan and Donald L.M. Blackmer
Little, Brown, 1961
Buku Teks