Weber, Engen
D. C. Heath, 1959
Buku Teks
David Boucher, Paul Kelly, editor
Oxford Univesity Press, 2009
Buku Teks
Weber, Eugen, author
D. C. Heath, 1959
Buku Teks
Sharma, R.P., author
Sterling Publishers Private, 1984
Buku Teks
Niles, Olive S., author
Georgia Scott 1984
Buku Teks