Classify each of the following examples as a cost of searching, bargaining, or enforcing an agreement to purchase a 1957 Chevrolet:

a. Haggling over the price.

b. Collecting the monthly payments for the purchase of the car.

c. Taking time off from work for the buyer and seller to meet.

d. Purchasing an advertisement in the "classified" section of the newspaper.

e. Purchasing a newspaper to obtain the "classified" section.

f. The buyer asking the seller questions about the car's ignition system.