Sheahan, John
University Press 1963, 1963
Buku Teks
Bechhoefer, Bernhard G., author
Brookings Institution, 1961
Buku Teks
St John, Maggie Jo
Prentice Hall ELT, 1994
Buku Teks
Hackett, John T.
Harvard University Press , 1963
Buku Teks
Hackett, John
Harvard University Press, 1965
Buku Teks