The Following Graph Shows a Firm's Long-Run Average and Marginal

The following graph shows a firm's long-run average and marginal cost curves.

-From zero to 600 units of output __________ exist. Beyond 600, ________________ exist. Suppose the firm decides to build a plant to produce 900 units of output at the least possible cost. After the plant is built the firm is in the short run with short-run average and marginal cost curves of ATC and MC. (ATC and MC are not shown in the figure.)