Which of the following is a pure public good?

Historical note: When the railroad displaced water transport as the principal means of long-distance transportation, it sparked massive investment spending not only in the railroad industry, but in secondary industries such as

a. mining, automobiles, and genetic engineering b. steel, computers, and videocassette recorders c. lumber, construction, and aviation d. construction, steel, housing, and semiconductors e. mining, steel, lumber, and construction

A firm's total cost divided by its level of output is equal to its:

A. average total cost. B. marginal cost. C. variable cost. D. start-up cost.