Stephenson, Carl
Great Seal Books, 1956
Buku Teks
Sharma, Ram Sharan, author
Macmillan, 1980
Buku Teks
Stephenson, George E.
Delmar, 1986
Buku Teks
Milsom, S.F.C.
Cambridge Uiversity Press, 1976
Buku Teks
Golden, Harry, author
World Pub., 1961
Buku Teks