Foreword by Wong Lian Aik
Center for English Language Communication. NUS, 2001
Buku Teks SO
Nasr, Raja T.
Longman, 1975
Buku Teks SO
Springer, 2016
Buku Teks
Bailey, Kathleen M.
Cambridge University Press, 2006
Buku Teks SO
Coxon, Rosemary
Letts Educational, 1994
Buku Teks SO