I want to know the answer to the following question:
How many of the main Mexican airlines are based in Mexico City?
All the background I'm provided with is that "In the Mexico City airport, the government engaged in an extensive restructuring program that includes the addition of a new second terminal, which began operations in 2007, and the enlargement of four other airports (at the nearby cities of Toluca, Querétaro, Puebla and Cuernavaca) that, along with Mexico City's airport, comprise the Grupo Aeroportuario del Valle de México, distributing traffic to different regions in Mexico.". Is that enough to answer the question?