Consider the following relational database:

flight (flight-no, source-airport, destination-airport) reservation ( passenger-ssn, flight-no, class) airport (airport-name, city)

Give the corresponding SQL queries for each of the following. (a) Find the airport names that have been destination of at least one flight that has not been reserved by passenger with id 999.

(b) Find the average number of business-class flights for the passengers.

(c) Find the passengers that have more number of flights than the number of Ankara-Berlin flights of each passenger.