Since the deregulation of airlines, delays at the nation' s increasingly busy airports have increased by 25 percent. To combat this problem, more of the takeoff and landing slots at the busiest airports must be allocated to commercial airlines. Which of the following, if true, casts the most doubt on the effectiveness of the solution proposed above? ["The major causes of delays at the nation's busiest airports are bad weather and overtaxed air traffic control equipment.", 'After a small Midwestern airport doubled its allocation of takeoff and landing slots, the number of delays that were reported decreased by 50 percent.', "Since deregulation the average length of delay at the nation's busiest airports has doubled.", "Over 60 percent of the takeoff and landing slots at the nation's busiest airports are reserved for commercial airlines."]