Which sentence in the text helps the reader understand its text structure?

O'Hare has about 1,028 direct domestic flights and 126 direct international flights each day.
While both airports are kid-friendly, O'Hare provides a special interactive children's area.
These trains travel over 2.7 miles of track and can carry 2,400 passengers in an hour.
The airport only has three concourses, making travel between gates easily accessible.