Erin Reinhardt and her friend Carol Newman have just arrived in the country Bologna for a summer holiday.
While renting a car on their first day in Bologna they notice that the car rental rates are so much higher than rates back home.
Carol says that in a matter of time, competition should drive prices down. Erin feels that the market for car rentals is probably competitive enough; it could just be the high cost of operations in Boloni that are responsible for the high prices.

Which of the following, if true, would weaken Erin's argument that high costs are responsible for high prices?

a. The car rental industry in Boloni is valued at $50 million.
b. Most households in Boloni own at least one car.
c. After global oil prices increased, the government of Boloni decided to ration the quantity of gasoline sold.
d. Only 3 firms account for almost 88 percent of the car rental market.
e. Most of the growth in the car rental industry comes from the high-value rentals of luxury cars.

Erin says that rental rates are high because the cost of running car rental companies is very high in Boloni, but if 88% of the market is controlled by only 3 companies, then the lack of competition is responsible for the high prices. The car rental market in Boloni is an oligopoly since the 3 big firms control the prices and probably keep them artificially high due to their market power.