Plant Sizes Get Larger as You Move from ATC-1 to ATC-4

Plant sizes get larger as you move from ATC-1 to ATC-4. Over what range of output are economies of scale experienced by this firm?

A) 1,500 to 3,000
B) 1,500 to 3,500
C) 2,000 to 3,500
D) 2,000 to 4,000