In Correlational Research,the "Third Variable Problem" Refers to a Circumstance

In correlational research,the "third variable problem" refers to a circumstance in which

A) scatter plots for positive,negative,and zero correlations are the same.
B) correlation between variables equals causation.
C) a variable that has not been measured accounts for the relationship between two other variables.
D) experimenter bias increases the effects of research participant bias.