Following are five series of costs A through E measured at various volume levels. Examine each series and identify which is fixed, variable, mixed, step wise, or curvilinear.

Volume (Units)

Series A

Series B

Series C

Series D

Series E

0

$0

$2,500

$0

$2,000

$4,000

200

3,600

3,100

6,000

2,000

4,000

400

7,200

3,700

6,600

4,000

4,000

600

10,800

4,300

7,200

4,000

4,000

800

14,400

4,900

8,200

6,000

4,000

1,000

18,000

5,500

9,600

6,000

4,000

1,200

21,600

6,100

13,500

8,000

4,000