What is the least likely outcome for a firm enjoying a monopoly in an industry that has a continually falling long-run average cost curve?

[1] The government regulates the firm as a monopoly.

[2] Buyers find ways to acquire a non-monopoly price from the producer by having a group purchasing agent to do the buying.

[3] The firm charges a monopoly price and goes unchallenged.

[4] Buyers contract with a new producer to provide a market in exchange for a less than monopoly price or the fear of this possibility keeps the monopolist from profit maximising.