Which market model assumes the least number of firms in an industry?

Refer to Table 16-3. Suppose Julie's marginal cost of providing this service is constant at $7 and she charges $7 per hour. What is her marginal revenue?

A) It is $7 for the first hour and starts increasing thereafter. B) It is constant at $7. C) It coincides with the figures in the table; $12 for the first hour, $10 for the second, $9 for the third, and $8 for the fourth. D) It is $7 for the first hour and starts declining thereafter.

Explain the three lags that make it difficult to time changes in discretionary policy properly