Lesson 4 背景知识听力填空Listen and fill in the blanks with proper words based on what you have heard.[音频]Control towers are established to provide for a _____, ______ and ______flow of air traffic at an airport and in its ____.The functions of an aerodrome control tower are generally performed by ______different ______ depending on the local procedures. They are______ controller, _____ controller and ______ controller.Controllers working in an airport control tower are ______ through each position during one work ____. Each of these positions has________.The Delivery is responsible for obtaining and ____________ to IFR flights.The Ground controller is normally responsible for traffic on the airport _______. These include all ______, _______ and some ______ areas or _______ or the departure gates.The Tower controller is also called local controller and he is in charge of ______ on the _____ as well as the air traffic in the vicinity of the airport.