Herrick, Glenn W. (Glenn Washington), 1870-1965, author
Comstock Publishing Company, 1935
Buku Teks
Attenborough, David
BBC Worldwide Limited, 2004
Multimedia
Thomas, Peter A., 1957-, author
Cambridge University Press, 2014
Buku Teks
Williams, Katie, author
Chronicle Books, 2010
Buku Teks
Vermeulen, Nico
Rebo Publishers, 1994
Buku Referensi