Grodinsky, Julius
Ronald Press , 1953
Buku Teks
Nwogugu, E.I.
Manchester University Press , 1965
Buku Teks
Sharpe, William F., author
Prentice-Hall, 1978
Buku Teks
Sharpe, William F., author
Prentice-Hall, 1990
Buku Teks
Gup, Benton E., author
John Wiley , 1979
Buku Teks