Question

correlation means that
two variables have a positive correlational coefficient.
one of the variables being measured must have caused the other one to change.
a third variable is always responsible for the changes of the first two variables.
two variables change together.
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Explanation:

Correlation indicates a relationship where two variables vary together. It doesn't imply causation (so the second and third options are wrong), and it can be positive or negative (so the first option is too narrow).

Answer:

two variables change together.