Answer:
Greetings!
The correct answer is the last one, "When the future level of some variable is seen as a function other than time".
Explanation:
Along other forecasting methods, the moving average finds utility in cases when seasonality is a factor. This term refers to a set of variables unknown to (or uncontrolled by) the observer that influence the series model in some way.
By applying a moving average to a time series one can mitigate such irregular effects.
I hope this helps!