To Identify Potential Moderator Variables for an Integrative Literature Review

To identify potential moderator variables for an integrative literature review one can

A) see if the theory that guided the research being reviewed includes any moderating variables.
B) look at previous research on the topic to see if any moderator variables were found in those studies.
C) use logic and one's knowledge of existing theory and research to identify potential moderator variables that have been overlooked.
D) do any of the above.