1. (2021九下·温州竞赛) 阅读理解

The basic aerodynamics used to make a paper airplane is very similar to the aerodynamics of a real plane.

A simple piece of paper will fall down when it is dropped. But if we fold the paper in a specific manner, it will fly. There are four types of forces in physics that play important roles in making a paper airplane soar in the air.

Surely lift is a force that holds the airplane in the air. It acts directly against the weight of the airplane. Though the whole plane uses this force, the wings are the ones that bring it to the maximum*level. Both the upper and lower surfaces of the wings are responsible for turning the flow of air.

Thrust is the forward force that is used to push the airplane in the forward direction. It comes from the engines of a real aircraft, but for a paper airplane, the human and artificiality produces this force while throwing the plane hard into air.

Drag, also known as air resistance*, is a force to pervert an object moving in gas or liquid. This force stops the movement of the aircraft in air. It occurs due to the surface friction*between the solid surface of the airplane and air molecules*.This too acts through the center of pressure of the object.

Another force is gravity acting on the airplane and continually trying to pull it down towards the earth. A real aircraft makes use of many lift, drag, and thrust forces against the gravitational force. In case of a paper airplane, when we fly it in the air with some energy, it uses that energy to stay in air for some time. As the energy goes on reducing, the plane moves downwards. As a result, the airplane fails to remain in the sky when all the energy is exhausted.

The wetness of the air also has a great effect on the flight of a paper airplane. As paper takes in water, it changes the density*of the airplane finally. So making the airplane out of a thick piece of paper proves to be more effective.

A real plane has additional parts used for efficient flying. To some degree, the weight of the passengers and luggage affect the above types of forces. Therefore, next time you make a paper airplane, keep in mind these points to make one that has a long-lasting flight.

1. （1） The force of lift is used by ____________ to hold the airplane in the air.

   A . only the wings B . the engines C . both the surfaces D . the whole plane
3. （2） Which is the right chart showing the four types of forces?

   A . B . C . D .
5. （3） The underlined word "exhausted" in Paragraph 6 most probably mean:" ____________".

   A . used up completely B . filled up immediately C . pushed forward heavily D . acted on the plane strongly
7. （4） According to the passage, which of the following statements is TRUE?

   A . A real aircraft can only make use of one or two types of the forces mentioned. B . The paper plane made out of thick paper is unable to have a long-lasting flight. C . Aerodynamics studies the movements of the air and the moving object in the air. D . Compared with sunny days, the paper plane can fly much farther when it is wet.