Falmer Press, 1996
Buku Teks
Watson, Jane
Sense, 2012
eBooks
Ben-Chai, David, author
Sense, 2012
eBooks
UNESCO, 1953
Buku Teks
John Sikula, senior editor ; Thomas Buttery, editor, Edith Guyton, editor
Macmillan Library Reference USA, 1996
Buku Referensi