Siagian, Sondang P., author
Gunung Agung, 1995
Buku Teks
Radford, K.J., author
Phoenix Press, 1981
Buku Teks
compiled by David R. Hampton
Prentince-Hall of India, 1979
Buku Teks
Alexander Hamilton Institute
Alexander Hamilton Institute, 1971
Buku Referensi
Stephen A.Ross
Mc Graw Hill, 2009
Buku Teks