Which of the following statements about variables cost are incorrect?

i. Costs that, in total, are constant within the relevant range as the level of the cost driver varies.

ii. Costs that, in total, vary in direct proportion to changes in a cost driver

iii. Per-unit variable costs change as the level of cost driver changes.

iv. At zero units produced, total variable cost is zero.

Select one:

a. i, ii, iii and iv

b. ii and iv

c. i and iii

d. ii and iii