Ryga, George
Talonbooks, 1976
Buku Teks
Ryga, George
General Publishing Co., 1982
Buku Teks
Beal, George M.
Iowa State University Press , 1962
Buku Teks
Troxell, George Earl, author
McGraw-Hill, 1968
Buku Teks
Salomon, Pierre, author
Paris Hatier-Boivin 1953
Buku Teks