Suppose the firm depicted below has two types of customers but cannot tell which type of buyer the customer is before a purchase is made. If the firm wanted to use second-degree price discrimination, it should charge _____ per unit for any quantity purchased or _____.

a. $12; $4 per unit for 4 or more units

b. $12; $7 for 3 or more units, but the pricing scheme would not be incentive-compatible for TypeB customers

c. $7; $4 for 2 or more units, but the pricing scheme would not be incentive-compatible for TypeA customers

d. 8.50; $4 for 3 or more units

\f