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?

The costs of direct materials are classified as:

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 $$

$$