(3)3.a. A table has six fields, express the projection mapping to remove both the second and fifth field. 3.b. What is the best choice for a primary key field of the following relation: BarCodeNumber, Product Name, Quantity, Price 3.c. Identify the clauses of this SQL statement which correspond to the selection, projection and join operations of a n-ary relation? SELECT FlightNumber, Origin, Destination, Seat, PassengerName FROM Flights, PassengerReservations WHERE DepartureTime = 0930