4- The following data have been collected for four different cost items. Cost at Cost at 140 units Cost Item 100 units 8,000 5,000 6,500 6,700 10,560 5,000 9,100 8,580 $ $ Which of the following classifications of these cost items by cost behavior is correct? The costs of direct materials are classified as: Cost Y mixed Cost W variable Cost X fixed Cost Z variable mixed A- mixed fixed variable B- variable variable mixed fixed fixed variable mixed C- mixed D