Cotterell, John
Lorenz Books, 2000
Buku Referensi
Harris, Stephen L, 1937-2004
McGraw-Hill, 2012
Buku Teks SO
Cooper, Hazel Dixon
Torrent Books, 2004
Buku Teks SO
Sykes, Egerton
J.M. Dent and Sons, [Date of publication not identified]
Buku Referensi
edited by Robert DeMaria and Robert D. Brown
Blackwell, 2007
Buku Teks SO