Answer:
Option a is right.
Step-by-step explanation:
When we do forecasting i.e. estimating before it really happens we come across the situations where actual will slightly deviate from the forecast value.
This difference i.e. actual or real value - predicted value is called the forecast error.
Here hence option a is right.
Option b is wrong because we subtract only fitted value from real value
Option C is wrong because the independent and dependent variable has nothing to do with forecast error.
D is wrong because the period difference is not forecast error
