Soltau, Roger H.
Longmans, Green , 1951
Buku Teks
Soltau, Roger H.
Longmans, Green , 1960
Buku Teks
The Free Press, 1990
Buku Teks
Schlesinger, Arthur Meier, author
Houghton Mifflin, 1962
Buku Teks
Montemayor, Jeremias U., author
Rex Book Store, 1976
Buku Teks