Russell, Frederick A.
McGraw-Hill Publishing Company, 1988
Buku Teks
Russel, Frederic A.
McGraw-Hill, 1955
Buku Teks
Russell, Frederic A.
McGraw-Hill, 1959
Buku Teks
Nixon, H.K.
McGraw-Hill, 1931
Buku Teks
Whiting, Percy H.
Dale Carnegie & Associates, Inc., 1979
Buku Teks