Which of the following statements is true

a. The fixed cost spending variance is the difference between the amount of fixed cost shown on the static budget and the fixed cost shown on the flexible budget

b. The foxed cost spending variance explains how volume affects fixed cost per unit

c. The fixed cost spending variance is the difference between the amount of fixed cost shown on the flexible budget and the actual amount of fixed cost

d. Since fixed costs do not change with volume, the fixed cost spending variance is always equal to zero.