Artikel Jurnal
Burrell, R.E.C.
Wheaton , 1980
Buku Teks
Ika Darnhofer, editor
[, Springer], 2012
eBooks
Leigh Brownhill, Esther M. Njuguna, Kimberly L. Bothi, Bernard Pelletier, Lutta W. Muhammad and Gordon M. Hickey.
Routledge, 2016
Buku Teks
Hatch, Mark, author
McGraw-Hill , 2014
Buku Teks