Cornog, Mary Wood, author
Merriam-Webster Inc., 1994
Buku Referensi
Zhao, Wanxun
Cengage Learning Asia, 2012
Buku Teks
Bauer, Lauria
London : Routledge, 1998
Buku Teks
Morgan, John, 1944-2004, author
Oxford University Press, 1990
Buku Teks
Woodson, R. Dodge, author
McGraw-Hill, 2009
Buku Teks