In Which Research Situation Below Would an Extraneous Variable Become

Multiple Choice

In which research situation below would an extraneous variable become a confounding variable?

A) An extraneous variable varies systematically along with the two variables being studied.
B) Two or more extraneous variables vary systematically with each other.
C) An extraneous variable is not directly investigated as part of the research question.
D) There are more than two extraneous variables present.