4. Until the 1980s, AT&T held a monopoly over the national market for phone services. Suppose that AT&T argued that it was a natural monopoly, because the fixed cost of creating a nationwide phone network generated huge economies of scale, and that there was therefore no welfare loss associated with its monopoly. Counter this argument by explaining how even a natural monopoly causes deadweight loss. 5. Explain why an oligopolist (with few competitors) pays more attention to what its competitors are doing than a producer in a competitive market (with many competitors) does.