A characteristic of a variable cost is:

a. the total cost varies in proportion to changes in the level of activity.

b. the cost per unit remains constant, regardless of the level of activity.

c. both the total cost varies in proportion to changes in the level of activity and the cost per unit remains constant, regardless of the level of activity.

d. Neither the total cost varies in proportion to changes in the level of activity nor the cost per unit remains constant, regardless of the level of activity.

(answer a is incorrect)