Identify each of the following statements with fixed costs or variable costs by writing fixed or variable in the space provided.
______ a. A cost that varies in total with changes in the activity level.
______ b. A cost that varies on a per-unit basis with changes in the activity level.
______ c. A cost that remains fixed per unit with changes in the activity level.
______ d. A cost that remains fixed in total with changes in the activity level.