Lewis, Norman
Harper & Row , 1962
Buku Referensi
Basch, Lester D.
Sterling Publishing , 1962
Buku Teks
Carney, Edward, translator
Routledge,, 1997
Buku Teks
Furness, Edna L.
Appleton Century , 1964
Buku Teks
Ur, Penny
Cambridge University Press, 1988
Buku Teks