Roper, Nancy
Churchill Livingstone , 1976
Buku Teks
Ashby, Eric
Stanford University Press, 1978
Buku Teks
Rotterdam University Press, 1974
Buku Teks
Boughey, Arthur S., author
McMillan Publisher, 1975
Buku Teks
Voice of American Forum Lectures, 1968
Buku Teks