Vega, Connie de la, author
Edward Elgar Publishing, 2013
Buku Referensi
United Nations, 1988
Buku Teks
Carey, John, author
Oceana Publications, Inc, 1968
Buku Teks
Digumarti Bhaskara Rao
Discovery Publishing House, 2001
Buku Teks
Digumarti Bhaskara Rao
Discovery , 2001
Buku Teks