Laski, Harold J.
George Allen and Unwin, 1952
Buku Teks
Green, John Richard, editor
New York The Co-operative Publication Society [t.th.]
Buku Teks
Rose, Richard, 1933-
Scott, Foreman, 1989
Buku Teks
Cash, Allen J.
The Automobile Association, 1987
Buku Referensi
Stroud, Angus
Routledge, 1999
Buku Teks