Ward, John
Routledge , 1997
Buku Teks
Vallier, Ivan
Prentice-Hall, 1970
Buku Teks
edited by Eduardo P. Archetti
MacMillan Education, 1987
Buku Teks
edited by, Dwight B. Heath and Richard N. Adams
Random House, 1965
Buku Teks
Burns, E. Bradford
Prentice-Hall, 1977
Buku Teks