Sometimes, a Systematic Search Procedure Yields Too Few Studies for Inclusion

Multiple Choice

Sometimes, a systematic search procedure yields too few studies for inclusion into a systematic review or meta-analysis. All of the following are good reasons for this, EXCEPT:

A) There are too few databases for searching for relevant studies.
B) The criteria for the search and selection of studies are too narrow.
C) Too few studies have been conducted on the topic of interest.
D) Too few studies used a strong enough methodology like a randomized controlled trial.