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