Figure 13-12

Figure 13-12
-Refer to Figure 13-12.If the figure in panel (a) reflects the long-run equilibrium of a profit-maximizing firm in a competitive market,the figure in panel (b) most likely reflects

A) perfectly inelastic long-run market supply.
B) perfectly elastic long-run market supply.
C) the entry of firms into the industry when some resources used in production are available only in limited quantities.
D) the fact that zero profits cannot be sustained in the long run.