ILO, 1984
Buku Teks
Nobes, C.W., author
Philip Allan/St. Martin Press, 1988
Buku Teks
James R. Hines, edited
The University of Chicago Press, 2001
Buku Teks
Nehr, Lee Charles, author
International Textbook, 1967
Buku Teks
Nehr, Lee Charles, author
Intext Educational, 1972
Buku Teks