Tanner's Gifts had the following costs in March when 400 ceramic statues were produced: $4,200 materials; $1,600 labor costs; $800 depreciation; $700 rent; $500 other fixed costs. If production changes to 500 units and production stills remains within the relevant range, which of the following costs will stay the same?

a. variable cost per unit

b. fixed cost per unit

c. total variable cost

d. total cost per unit

e. none of these answer choices is correct