Why Is It Unwise to Conclude That If Two Variables

Multiple Choice

Why is it unwise to conclude that if two variables are correlated, one must have caused the other?

A) Variables can never be measured with complete accuracy.
B) Any single variable is bound to have multiple causes.
C) Some unmeasured third variable might make them appear related when in fact they are not.
D) It is impossible to conclude that two variables are related unless one can measure them perfectly.