Foreword by Wong Lian Aik
Center for English Language Communication. NUS, 2001
Buku Teks SO
Jesus Romero-Trillo
Springer, 2012
eBooks
Morris, I.
Macmillan, 1950
Buku Teks
edited by James Flood, Julie M. Jensen, Diane Lapp, James R. Squire
Macmillan, 1991
Buku Referensi
Springer, 2016
Buku Teks SO