In the Long Run for Firm A,total Cost Is $105

In the long run for Firm A,total cost is $105 when output is 3 units and $120 when output is 4 units.Does Firm A exhibit economies or diseconomies of scale?

A) Diseconomies of scale, since total cost is rising as output rises.
B) Diseconomies of scale, since average total cost is falling as output rises.
C) Economies of scale, since total cost is rising as output rises.
D) Economies of scale, since average total cost is falling as output rises.