Ramsey, Douglas K.
Houghton Mifflin, 1987
Buku Teks
Haith, Douglas A.
Wiley, 1982
Buku Teks
Foster, Douglas
Macmillan, 1985
Buku Teks
Lowndes, Douglas
Pergamon Press , 1969
Buku Teks
Adams, Douglas, 1952-
Oxford Heinemann New Windmills 1991,
Buku Teks