Croft, Kenneth
Mass. Winthrop , 1972
Buku Teks
Byrd, Patricia
Prentice-Hall, 1981
Buku Referensi
Lugton, Robert C.
Prentice-Hall, 1978
Buku Teks
Gunter Narr Verlag, 1980
Buku Teks
Birgit Harley...[et al.], edited
Cambridge University Press , 1990
Buku Teks