Malmstrom, Jean
National Council of Teachers of English , 1963
Buku Teks
Wolfram, Walt, 1941-
Wiley Balckwell, 2016
Buku Teks
Upton, Clive
Routledge, 2006
Buku Referensi
edited by Peter Trudgill and J.K. Chambers
Longman, 1991
Buku Teks
1997
Buku Teks