Birmingham, David
Cambridge University Press, 1993
Buku Teks SO
Livermore, H.V.
Cambridge University Press, 1969
Buku Teks SO
Disney, A.R
Cambridge University Press, 2009
Buku Teks SO
Torga, Miguel
Rua Cintura do Porto, 2003
Buku Referensi
Disney, A. R. (Anthony R.), 1938-
Cambridge University Press, 2009
Buku Teks SO