Moody, Richard, author
Chancelor, 1994
Buku Teks
Henslow, John Stevens, author
cambridge University Press, 2013
Buku Teks
Wagner, Scott A., author
CRC Press, Taylor & Francis Group, 2009
Buku Teks
USAID, 2003
Buku Teks
Clark, William S., author
Houghton-Miffiln, 1987
Buku Teks