Artikel Jurnal
Gavin Bennett, Nasreen Jessani, editor
Sage, 2011
Buku Teks
Shepard, Steven, author
McGraw-Hill, 2002
Buku Teks
Smith, Brenda D., author
Longman, 2000
Buku Teks
Lean Mei Li, Mya Khemlani David, Ngew Yeok Meng, editor
University of Malaya, 2011
Buku Teks