In his lecture on learning objectives, Dr. Carr lists these as the "Preferred and Sufficient" sources for information to include in your LO.
Textbooks (see Books tab for more)
Web-based articles (i.e. websites) where the author, references, date updated are listed. Organizations such as the CDC, Mayo Clinic, American Cancer Society usually do not meet this criteria because no author is listed. Check the References to find any articles they may have quoted in order to get to primary literature.
Primary literature (i.e. journal articles) from reputable journals. (See Articles tab for more.)