A、Its private airline service. B、Being an American Post Office. C、Its transporting small packages. D、The low cost of its service

Federal Express is a private airline service. It expands the Postal Service in the United States. It is the only U. S. airline specializing in the transportation of small packages--35 kilograms or less.
    Federal Express links 130 major American cities and 10000 surrounding communities. An urgent package picked up in one part of the country this afternoon can be delivered to any other part of the country tomorrow morning. All of the Federal Express jets fly into the International Airport at Memphis, Tennessee, because it is located in the center of the United States.
    The sorting system for Federal Express is called "The Hub". Every night, from about 12 midnight to 3 am, the packages are gathered and sorted into shipments for specific destinations. The main labor force is comprised of students working part-time.
    Since Federal Express started business in 1971, it has flown millions of air kilometers without fail. In the space of one hour, 39 jets will take off to destinations all across the country.
26. What makes Federal Express different from other airlines in America?
27.How many important U. S. cities does Federal Express link?
28.Why do all Federal Express planes fly into the International Airport at Memphis, Tennessee?