Abboud, Peter F
Cambridge University Press, 1983
eBooks
Ryding, Karin C
Cambridge University Press, 2013
Buku Teks
New York Cambridge University Press 1983,
Buku Teks
Wehr, Hans, 1909-1981
Spoken Language Services, 1976
Buku Referensi
Starkey, Paul
Edinburgh University Press, 2006
Buku Teks