Which of the Following Is an Advantage of Including Only

Which of the following is an advantage of including only published studies in a literature review?

A) Studies that find null results are often not published, preventing such low-information studies from becoming a distraction.
B) The peer review process provides a check on the internal validity of published studies.
C) The information in published studies is generally more useful than information in unpublished research.
D) Published studies are more likely to be based on results that contradict accepted theories.