One of the largest airports in the world is in Grapevine, Texas, midway between the cities of Dallas and Fort Worth. This airport covers 7 200 hectares (18 000 acres).Its five terminals can handle the arrivals and departures of 90 jumbo jets at the same time. O’Hare International Airport, in Chicago, is the busiest airport in the world. It handles more than 37 million passengers a year.

　　Small airports that are used only by private airplanes usually cover 20 to 40 hectares (50 to 100 acres).They do not need all the buildings and services of a large airport. The control tower may be just a small room in a building at ground level.

　　Runways

　　Early planes were light. Early runways were sometimes just level grass fields. Paved runways became necessary when airplanes became heavier and faster. Today’s big jet planes weigh hundreds of tons. They move along runways at speeds of 160 kph (100 mph).When they land, the runways take a lot of pounding and must be made of concrete or asphalt(瀝青).They must have solid foundations and a surface that prevents skidding.

　　Airplanes take off into the wind in order to get better lift. They also land into the wind to have better control as they slow down. Most airports have runways pointing in different directions. This means that there are always runways on which airplanes can go into the wind as they take off and land.

　　Heavily loaded passenger jets need long runways to gather enough speed to leave the ground. Runways at some large airports are longer than 3 000m(10 000 ft).

　　At night, bright lights line the runways so that pilots can find them without trouble. A system of flashing guide lights is set up beyond the runway to help pilots land safely.

　　Control Towers

　　People who work in control towers are called air traffic controllers. They direct the movements of all planes on the ground and in the air by keeping track of them on large radar screens. Air traffic controllers tell a pilot, by radio, when and where to taxi or pilot the plane down the runway.

　　Electronic equipment is used to guide airplanes. Long range radar is used to keep track of planes far away from the airport. This radar is called Ground Control Approach (GCA).When the airplane gets within a few miles of the runway, the air traffic controller begins to use Precision Approach Radar (PAR).This allows the controller to guide the airplane to within 0.4km(0.25mi)of the runway. At that point, the pilot completes the landing. Another electronic aid used in bad weather is the Instrument Landing System (ILS).In this system, radio transmitters located near the runway send guidance signals to the airplane. These signals tell the pilot how to steer the plane for the final approach to the runways. Today, there are also electronic “microwave” landing systems (MLS) that can land the plane fully automatically.

　　Terminal Buildings

　　Terminal buildings vary in size and shape. Most of them are quite large. More than 228 million people fly on the airlines in America every year. Every passenger must pass through terminals. Long, covered walkways lead from the center of some terminals to the gates where airplanes are boarded. At some airports, buses are used to transport passengers to their airplanes. Passengers arriving from another country must pass through customs and passport control. Customs officials check the incoming baggage for taxable items. They also check passengers to be sure no forbidden items are brought into the country. Passport officials check the passports of passengers for personal identification.

　　Passengers are not allowed to bring guns, knives, or other weapons onto a passenger airplane. Before boarding, they must walk through a detector which triggers a special signal if they are carrying anything made of metal. Luggage is also examined for weapons. This is done to ensure the safety of the passengers.

　　1. The main purpose of this passage is to introduce the history of airplanes.

　　2. The device of an automatic pilot can usually fly a plane more smoothly than a human pilot.

　　3. With the help of the radio equipment, pilots are able to communicate with ground controllers.

　　4. We can tell from the passage that early airplanes are not as solid as modern ones.

　　5. According to the passage, the busiest airport in the world is in Grapevine, Texas, midway between the cities of Dallas and Fort Worth.

　　6. The runways should be long and solid enough for the heavily loaded jets.

　　7. Precision Approach Radar (PAR) is used by air traffic controllers to keep track of airplanes far away from the airport.

　　8. The planes can be landed fully automatically if the control towers are equipped with .

　　9. After getting off the plane, every passenger arriving from another country must pass through .

　　10. When passengers go through a detector before they board, and anything made of metal is detected, the detector triggers .