Arblaster, Anthony
Open University Press, 1987
Buku Teks
Schulz, Ernest B
[publisher not identified], 1956
Buku Teks
Pritchard, Elizabeth
Stanford university press, 2014
Buku Teks SO
Korean Overseas Information Service, 1978
Buku Teks SO
Oxford University Press, 1995
Buku Teks