Rowley, Jennifer
Kogan Page, 1991
Buku Teks
Saphier, Michael
New York: McGraw-Hill, 1968
Buku Teks
Eyre, E.C.
Macmillan, 1989
Buku Teks
Littlefield, C. L.
Prentice-Hall, 1956
Buku Teks
Kallaus, Norman Francis, 1924-, author
South-Western Publishing, 1987
Buku Teks