private void ActivateRefinery(IRefineryActivity activity)
        {
            bool hasRequirement = activity.HasActivityRequirements(); // if the requirements for the activity are fulfilled

            if (hasRequirement)
            {
                currentActivity     = activity; // the activity will be treated as the current activity
                refinery_is_enabled = true;     // refinery is now on
            }
            else
            {
                activity.PrintMissingResources();
            }
        }