Bell, Richard
The Edinburgh University Press , 1953
Buku Teks
Page, Malcolm
Macmillan Education, 1987
Buku Teks
Roberts, Richard A., 1935-
Massachusetts Addison-Wesley, 1992
Buku Teks
Shultz, Richard D.
John Wiley & Sons, 1988
Buku Teks
Shultz, Richard D.
Harper & Row Pub., 1985
Buku Teks