At the current price of a good, Al's consumer surplus equals 15 and Ben's consumer surplus equals 15. By using two-part pricing, a monopolist could increase his profit by

Marginal cost

A. measures how total cost changes when input prices change. B. is less than average cost when average cost is decreasing. C. measures how total cost changes when one more unit of output is produced. D. both a and b E. both b and c 

The introduction of credit cards and debit cards has ________ velocity.

A. decreased B. increased C. eliminated D. had no impact on