Boodish, H.M., author
McGraw-Hill, 1949
Buku Teks
Delp, Mahlon
Philldedelphia: Wb sounder company , 1981
Buku Teks
Brookings institution, 1949
Buku Teks
Kinloch, Graham C., author
McGraw-Hill, 1977
Buku Teks
Major, Stephen P.
John Wiley & Sons. Inc., 1995
Buku Teks