If Someone Searches for a Flight Between Los Angeles and Chicago,he

If someone searches for a flight between Los Angeles and Chicago,he or she will find different airlines offering flights at similar prices.Why does this occur?

A) This occurs because one airline offers more flights at more convenient times than other airlines.
B) This occurs because the flights are filled primarily with workers from the largest 10 companies in each of the cities.
C) This occurs because there are many airlines and many different kinds of customers.
D) This occurs because the cities are far away from each other and not many would choose to drive between the two cities.
E) This occurs because passengers only pick those airlines where they collect frequent flyer miles.