Morris, Noel Malcolm, 1929-
Longman, 1980
Buku Teks
Robertson, Christopher R.
Edward Arnold, 1993
Buku Teks
Robertson, Christoper R.
London: Edward Arnold, 1993
Buku Teks
Hughes, Edward
Pearson Education, 2002
Buku Teks SO
Shrader, Robert L.
McGraw-Hill, 1977
Buku Teks