1. The short-run supply curve of a competitive industry is derived by

a. horizontally summing the average cost curves for each firm in the industry.

b. vertically summing the marginal cost curves for each firm in the industry.

c. horizontally summing the marginal cost curves for each firm in the industry.

d. vertically summing the average cost curves for each firm in the industry

2. Along the long-run supply curve of an increasing-cost industry that is characterized by perfect competition, all of the following can vary except

a. the level of profits.

b. the number of firms in the industry.

c. input prices.

d. the level of input usage.

3. For the case of an increasing-cost industry, supply is

a. more elastic in the long run than in the short run.

b. more elastic in the short run than in the long run.

c. more elastic the lower the input prices.

d. more inelastic in the long run than in the short run