Your instructor wants you to use scholarly [or 'peer reviewed'] sources. What does she mean?
Authoritative- written by a recognized expert in the field. How do you know? The PhD is one sign; employment by a university is another.
Peer reviewed- before publishing, the article was vetted by other scholars in the field. How do you know? Try searching the journal title in Google and read the publisher's blurb.
Audience- written for scholars and experts in the field. How do you know? The level of the language is usually a give away. It will be technical and formal.
Includes a bibliography and/or footnotes with citations of sources used.
Scholarship is always changing. Try to find the most recent scholarly sources you can.
Has been cited by other scholars. This can take time, so the newest articles might not be heavily cited yet. How do you know? Try searching the article citation in Google Scholar, which indicates the number of citations in Google Scholar [not comprehensive however]
Proves the point with sufficient evidence, rather than opinion statements.
