the answer is:
El agente de aduana abre las maletas para inspeccionarlas.
the other options do not apply because:
El copiloto has nothing to do with your luggage. He helps the pilot.
El equipaje de mano is an object and we need a subject to the verb abrir.
El asistente de vuelo is the same as the flight attendant and he or she is in charge of providing meals for and otherwise look after the passengers on a ship or aircraft.