Thatcher, W.S.
English University Press, 1957
Buku Teks
Wheeler, James O.
John Wiley & Sons, 1986
Buku Teks
Hartshorn, Truman Asa
Prentice-Hall, 1988
Buku Teks
Alexander, John W.
Prentice-Hall, 1979
Buku Teks
McCarty, Harold H.
Prentice-Hall, 1966
Buku Teks