Lambert, Kenneth A.
Course Technology, Cengage Learning, 2012
Buku Teks SO
Cambridge University Press, 2008
eBooks
Monro, Donald M.
Edward Arnold, 1974
Buku Teks SO
Bussmann, Hadumod
Routledge, 1996
Buku Referensi
Tsujimura, Natsuko
Blackwell, 2007
Buku Teks SO