Answer:
D. This agreement is not in the best interest of society, because there will be less competition and the price of cell phones will be significantly below marginal cost.
Explanation:
If the market for cell phones is an oligopoly market(Oligopoly market is a market situation where few firms are dominating the market), and the consumption and production of cell phone generate no negative externalizes and the major companies desired to collude and charge a single price for their product then this agreement is not in the best interest of society, because there will be less competition and the price of cell phones will be significantly below marginal cost.