Cook, Chris
Longman, 1991
Buku Referensi
edited by Ian Gregory, Don DeBats and Don Lafreniere
Routledge, 2018
Buku Teks SO
Routledge, 2021
eBooks
Palmer, Robert Roswell, 1909-2002
McGraw-Hill, 1992
Buku Teks SO
edited by Catherine Spooner, Emma McEvoy
Routledge, 2007
Buku Teks SO