The table shows three short-run cost schedules for three plants of different sizes that a firm might build in the long run. Plant 1 Output 10 20 30 40 50 B Plant 2 ATC $10 9 8 10 Plant 3 Output 10 - 20 30 40 50 ATC $15 10 10 14 A up to 10 units of output, and diseconomies of scale after that. up to 20 units of output, and diseconomies of scale after that. up to 30 units of output, and diseconomies of scale after that. Output up to 40 units of output, and diseconomies of scale after that 10 If the three plant sizes shown are the only ones possible, then there are economies of scale in producing 20 30 40 50 ATC $20 15 10 8 9