Barlow, Hugh D.
Litle, Brown and Company, 1984
Buku Teks
Slama-Cazacu, Tatiana
The Hague Mouton, 1973
Buku Teks
Robert, D.S.
Harper & Row, 1981
Buku Teks
Bryson, George D.
Harper & Brothers, 1961
Buku Teks
Musolf, Lloyd D.
Scott, Foresman and Company, 1965
Buku Teks