Hart, James D., author
Oxford University Press, 1986
Buku Referensi
Blair, Walter, author
Scott-Foresman, 1946-1947
Buku Teks
Edmundson, Mark, author
Cambridge University Press, 2011
eBooks
Gultom, Samuel, author
Greenwood Press, 1987
Buku Referensi
VanSpanckeren, Kathryn, author
Lembaga Penerangan Amerika Serikat, 2001
Buku Teks