Spradley, James P.
Halt, Rinehart and Winston, 1979
Buku Teks
Cambridge University Press, 1997
eBooks
Martin, Carole, author
McGraw-Hill, 2012
Buku Teks
Fletcher, John, author
Duckworth, 1973
Buku Teks
Atkinson, Paul, author
Routledge, 1994
Buku Teks