辐射雾常发生于（）中心。

Before the airplane begins to move, thrust must be exerted. It continues to move and gain speed until thrust and drag are equal. In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude. If in level, the engine power is reduced, the thrust is lessened, and the airplane slows down. As long as the thrust is less than the drag, the airplane continues to decelerate until its airspeed is insufficient to support it in the air.4.How many speed regimes are mentioned in the passage?

Before the airplane begins to move, thrust must be exerted. It continues to move and gain speed until thrust and drag are equal. In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude. If in level, the engine power is reduced, the thrust is lessened, and the airplane slows down. As long as the thrust is less than the drag, the airplane continues to decelerate until its airspeed is insufficient to support it in the air.3.When an aircraft descends, （ ）.

Before the airplane begins to move, thrust must be exerted. It continues to move and gain speed until thrust and drag are equal. In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude. If in level, the engine power is reduced, the thrust is lessened, and the airplane slows down. As long as the thrust is less than the drag, the airplane continues to decelerate until its airspeed is insufficient to support it in the air.2.If the air is to accelerate, （ ）.

Before the airplane begins to move, thrust must be exerted. It continues to move and gain speed until thrust and drag are equal. In order to maintain a constant airspeed, thrust and drag must remain equal, just as lift and weight must be equal to maintain a constant altitude. If in level, the engine power is reduced, the thrust is lessened, and the airplane slows down. As long as the thrust is less than the drag, the airplane continues to decelerate until its airspeed is insufficient to support it in the air.1.In order to maintain a constant airspeed, （ ）.

Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream. 5.The airplane flying west to east within jet stream will （ ） ．

Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream. 4.When we lower or raise the flap, the airplane will （ ） ．

Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream. 3.The article doesn＇t imply that the airplane can fly because （ ） ．

Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream. 2.The forces that act on a parking airplane include （ ） ．

Certain laws of nature are utilized in flight. The first requirement is the appropriate fly ing shape, or airfoil, which is commonly called the wing. This is shaped like a flattened teardrop. The rounded rear edge is called the trailing edge. The aircraft is supported by the earth’s atmosphere. What we think of as air is really a mixture of gases that have mass and weight but no shape.The forces that act on the airplane in flight are weight, lift, thrust and drag. Weight refers to the force of gravity that acts on the plane and everything in it at anytime. In order to fly, the plane must create a force stronger than the forces of its own weight. This is called lift. The lift is produced by the movement of the air around the wing as the plane moves through it. When the wing moves through the air quickly, a low pressure area vacuum is created on top of the wing, and a high pressure area is created under the wing. It is like a cushion of air on which the plane rests and stays during flight. An airplane propelled by the thrust of its jet engines can be thought of as flying on this cushion of air. Drag is the total resistance of the air to the aircraft passing through it. It may occur when the wing moves through the air to create lift, or it may occur when the landing gear is lowered.The pilot has controls that enable him to operate the plane as it moves through the air. He can cause it to ascend, descend, or remain level. He can also make turns in the air. This is called banking. The controls utilize the forces of the air by making slight adjustments or changes in the wings or the tails. When the flaps-the hinged sections of the wing are raised or lowered by the pilot, they can cause the aircraft to increase lift, decrease landing speed, and so forth. Similarly, changes in the tail of the aircraft cause the plane to turn to the right or to the left.Weather and atmospheric factors also affect flight. A headwind, or wind blowing a gainst the nose of the plane, will decrease speed. A tailwind will have the opposite effect. Altitude also affects flight. There is a huge river of wind that circles the globe generally from west to east at anywhere from 2500-50000ft above the surface of the earth. This is called the jet stream. As much as two hundred miles an hour may be added to the speed of a plane flying west to east within the jet stream.1.What might take place in your mind when you see airfoil?

Aircraft control systems are classified as primary and secondary. The primary control systems consist of those which are necessary for the safe flight of an aircraft, such as ailerons, elevator and rudder. Secondary control systems improve the performance feature of the aircraft or reduce the control forces by the pilots. Examples of secondary control systems are wing flaps and trim systems.The ailerons are located on the outboard trailing edges of both wings and are used to ro tate the aircraft around the longitudinal or roll axis. These surfaces move in opposite direc tions from each other and are controlled by rotation of the control wheel. When the control wheel is rotated to the left, the right aileron moves down and the left aileron moves up. This causes the airplane to roll to the left. When the control wheel is turned to the right, and op posite aileron movement results and the airplane rolls to the right.The pitch motion around the lateral or pitch axis is controlled by elevator moved by fore and aft movement of the control wheel. A change in position of the elevators modifies the camber of the airfoil which increases or decreases lift. When the pilot wants to raise the air craft nose, back pressure is applied on the control wheel. This moves the elevator up, result ing in a negative angle of attack. This causes the tail to move down and the nose of the air craft to move up. The rudder moves the aircraft about the vertical, or yaw axis resulting in a motion known as yaw. The movement of the rudder is to the left or to the right and is con trolled by the movement of the rudder pedal in the cockpit. Pressure applied to the right rud der pedal displaces the rudder to the right. This increases the camber on the left side of the vertical tail surface, creating a low pressure area on the left and a high pressure area on the right side. The resulting pressures cause the tail to move left and the nose of the aircraft to move right. Applying pressure to the left rudder pedal provides an opposite reaction. The rudder is used in conjunction with the ailerons to coordinate turns.5.Which of the following words can＇t be grouped together?