You may be asked to use peer-reviewed journal articles for your assignment. These are articles published in journals that require articles to be reviewed by a group of academics in the field before they are accepted for publication.
Databases with peer-reviewed journal articles:
Find highly ranked journals, grouped by field of research, in the ERA 2010 list.
Check a journal's ranking of in the Australian Business Deans Council (ABDC) Journal Quality List 2013 or the ERA 2010 list.