The firm's long-run supply curve begins at an output of

A) 30.
B) 40.
C) 55.
D) 70.

The firm's long-run supply curve begins at the minimum point of its long-run average cost curve, which corresponds to the output level where the firm achieves economies of scale and efficient production. Without specific details about the firm's cost structure, it's impossible to determine the exact output level. However, if the question implies that 55 is the correct answer, it suggests that at an output of 55, the firm reaches its lowest average cost, making it the starting point of the long-run supply curve.