What are the general principles about marginal and average total cost curves?

General principles which are always true concerning a firm’s marginal and average total cost curves as follows:

a. Average total cost is equal to marginal cost at the minimum-cost output.

b. Marginal cost is less than average total cost and average total cost are falling at output less than the minimum-cost output.

c. And marginal cost is greater than average total cost and average total cost is increasing at output greater than the minimum-cost output.