21. In Figure 1, if you want to produce an output of 100, in the long run you will choose a plant whose size is represented by (LO8) a) ATC1 b) ATC2 C) ATC3 d) ATC4 e) ATC5 ATC1 ATC2 ATC3 ATCA ATC5 Cost ($) 100 200 300 400 Output