$3.$ When airlines have already committed to significant upfront investments in aircraft and landing slots, it is rational to operate a flight if the marginal revenues the firm makes from the flight more than cover the variable costs of operating the flight. This makes it rational for airlines to compete on a route even if they cannot make profits above their total costs $($including both theses upfront fixed costs and variable costs$).$

The U$.$S$.$ airlines industry found itself in this postion in the late twentieth century. Given that description which of the following changes do you think would be most likely to improve airline profitability?

A$.$ Mergersiacquisitions that un airies to of mins im sompeting on the same routes

B$.$ Increased regulation requiring all air ra supperse passengers for late service

C$.$ A merger between airlines two key aircraft suppliers, Boeing and Arous