You Have Recently Submitted a Study for Publication and One

You have recently submitted a study for publication and one of the reviewers mentions that your study suffers from a third-variable problem. What do we know for sure about your study?

A) You used a repeated measures design.
B) You used a between subjects design.
C) You used a within subjects design.
D) There were three independent variables in your study.
E) Your study is correlational.