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An airplane flies because its wings push down on the air flowing past them, and in reaction, the air pushes up on the wings. When an airplane is level or rising, the front edges of its wings ride higher than the rear edges. The angle the wings make with the horizontal is called the angle of attack. As the wings move through the air, this angle causes them to push air flowing under them downward. A sleeper angle of attack will cause the wings to push more air downward. The third law of motion voiced by English physicist Isaac Newton states that every action produces an equal and opposite reaction. In this case, the wings pushing air downward is the action, and the air pushing the wings upward is the reaction. This causes lift, the upward force on the plane, Lift is often explained using Bernoulli’s principle, which states that, in some circumstances, a faster moving fluid(流体) (such as air)will have a lower pressure than a slower moving fluid. The air on the top of an airplane wing is at a lower pressure than the air underneath the wing, but this is an effect of lift, not its cause.Lift is one of the four primary forces acting upon an airplane. The others are weight, thrust, and drag. Weight is the force that offsets lilt. because it acts in the opposite direction. The weight of the airplane must be overcome by the lift produced by the wings, if an airplane weighs 4.5 metric tons, then the lift produced by its wings must be greater than 4.5 metric tons in order for the airplane to leave the ground. Designing a wing that is powerful enough to lift an airplane off the ground, and yet efficient enough to fly at high speeds over extremely long distances, is one of the marvels of aircraft technology. What are forces acting upon an airplane
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Passage 2Question 8 to 10 are based on the passage you have just heard.[听力原文]8-10In ancient Egypt, as everywhere, throwing stones was a favourite children’s game. But a badly thrown rock could hurt a child. Looking for something less dangerous to throw. what the Egyptians made were probably the first balls.At first, balls were made of grass or leaves held together by vines. Later they were made of pieces of animal skin sewed together and stuffed with feathers or hay.Even though the Egyptians like fighting, they found time for peaceful games. Before long they had developed a number of tall games, each with its own set of rules. Perhaps they played ball more for instruction than for fun. Ball playing was thought of mainly as a way to teach each young man the speed and skill he would need for war. At first, what were balls made of（）
[听力原文]M: You said the glasses fell on the floor, but I can’t find it.W: Just look under the, desk. What does the woman mean（）
A sick or injured person can obtain medical care in several different places. These include provider practices such as medical offices and clinics, hospitals and nursing homes.There are about 200,000 medical offices, clinics, and other provider practices in the United States. Earlier in the 20th century most physicians were single people working in their own offices or in partnership with another doctor. Patients visited the office, received an examination or other service, and paid a fee. This traditional fee-for-service medicine has been declining. Many physicians now practice in groups where they share the same offices and equipment with other doctors. Group practices may combine primary care physicians, several kinds of specialists, laboratories, and equipment for diagnosing disease. Physicians who practice in a group reduce their own expenses and provide patients with a wider range of services.Many doctors are joining with hospitals, insurance companies, and industrial employers to provide managed care for groups of patients. These plans manage to avoid unnecessary services and reduce costs. Rather than taking a fee from each patient, managed care physicians may receive an annual salary from a fixed sum for each patient.Patients who are too sick for care in a doctor’s office go to a hospital. Hospitals offer Patients 24-hour care from a staff of health professionals. They provide services not available elsewhere, such as major surgery, child birth, and intensive care for the critically ill. Hospital care is the most expensive form of health care. Efforts to control health care costs have emphasized reducing the number of patients admitted to hospitals and their length of stay. During the 1980s and 1990s, these efforts led to the closing of more than 600 hospitals.Patients who need long-term medical care because of advanced age or chronic illness may stay in a nursing home. The United States has about 23,000 nursing homes with about 1.3 million patients. Earlier in the 20th century, people often went to the（）to check the illness.
Passage 2Question 8 to 10 are based on the passage you have just heard.[听力原文]8-10In ancient Egypt, as everywhere, throwing stones was a favourite children’s game. But a badly thrown rock could hurt a child. Looking for something less dangerous to throw. what the Egyptians made were probably the first balls.At first, balls were made of grass or leaves held together by vines. Later they were made of pieces of animal skin sewed together and stuffed with feathers or hay.Even though the Egyptians like fighting, they found time for peaceful games. Before long they had developed a number of tall games, each with its own set of rules. Perhaps they played ball more for instruction than for fun. Ball playing was thought of mainly as a way to teach each young man the speed and skill he would need for war. What is the reason for ancient people to play bail（）
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