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  3. Transportation in the U.S. Railroads are paths of parallel metal rails that allow a wheeled vehicle to move more easily by r

Transportation in the U.S. Railroads are paths of parallel metal rails that allow a wheeled vehicle to move more easily by r

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问题                         Transportation in the U.S.
    Railroads are paths of parallel metal rails that allow a wheeled vehicle to move more easily by reducing friction. Iron mils were first used in the early 1800s to guide horse-drawn wagons. After the invention of the steam locomotive (机车) in 1804, steam engines replaced horses as the primary means of power. Modem locomotives commonly use electric motors or diesel (柴油机) engines and pull long trains of passenger or freight (货物) ears. The benefits of rail transportation in both speed and carrying capacity made it superior to other methods of transportation in the 1800s. In the United States and Canada, with their vast expanses of territory, the railroad became a major means of cross-country transportation. In many countries, rail continues to be the main mode of passenger travel. In Europe and Japan, major cities axe connected by high-speed passenger trains, such as the French TGV (Train Grande Vitesse) and the Japanese Shinkansen (新干线) trains, popularly known as bullet trains (高速火车). The Shinkansen train can reach speeds of 300 km/h (186 mph). Railroads have had a profound impact on civilization. Most importantly, the efficiency and speed of mil travel allow a nation’s population, industry, and agriculture to be established throughout that nation’s territory, even in previously remote areas. Rail transportation has also played a significant role in urban transportation systems.
    Motor vehicles make up a broad class of self-propelled (机动式的) land-transportation devices that generally use internal-combustion engines (内燃机) and gasoline or diesel fuel for power. Most motor vehicles are designed to travel on roads, but specialized vehicles with more solid construction are used for off-road travel over irregular ground. Motor vehicles range from motorcycles and automobiles for personal use to trucks, which can transport large amounts of cargo, and buses, which can carry many passengers. The first self-propelled vehicle was powered by steam. French engineer Nicholas-Joseph Cugnot built a steam-propelled vehicle in 1769. Between 1860 and 1890, innovations in steam-engine technology led to more steam-powered vehicles, primarily in France. At the beginning of the 20th century, gasoline powered automobiles began to emerge as the dominant form of motor vehicle. Automobiles and other motor vehicles grew especially popular in the United States. From a relatively modest number in 1900, the number of motor vehicles in the United States reached 458,500 by 1910 and 6.2 million by 1918. At the end of the 20th century, over 130 million automobiles, 69 million light trucks, and 1.2 million heavy trucks were in use in the United States, being driven an estimated 4.5 trillion km (2.8 trillion mi) per year. The heavy truck, which first came into mass production just prior to World War Ⅰ (1914-1918), has become a major means of moving freight. It is a major competitor with railroads for freight business. The bus was developed in response to the apparent popularity of tiding in motor vehicles. In many nations buses are a major form of urban and intercity passenger transportation. The motorcycle is one of the most abundant forms of individual urban transportation in the world today. The growth of motorcycle or motorbike use has been especially large in Asian cities, where motorcycles provide a means of bypassing crowded automobile traffic. One of the few motor vehicles that do not use wheels is the snowmobile, which uses a drive track (made of a belt of robber) and a pair of skis to move through snow. Although used for basic transportation in areas with heavy winter snows, the snowmobile is mostly used as a recreational vehicle. Over 200,000 snowmobiles are sold annually in the United States, Canada, and Europe.
    Air travel has revolutionized global transportation by dramatically reducing the time needed to travel great distances. Journeys across nations or oceans that might have taken weeks or months can now be made in a matter of hours. With large numbers of people traveling in airplanes, air transportation has become a major part of the world’s transportation system. Airplanes are heavier-than-air craft that use wings to produce lift in order to fly. Airplanes transport people from place to place and also ferry (运送) shipments of mail, fragile goods, and other important cargo. The airplane has also revolutionized warfare. Many aeronautical (航空学的) advances in technology, such as the jet engine, were achieved by military engineers and designers. The first sustained, piloted flight of an airplane was made in 1903 by American brothers Orville and Wilbur Wright at Kitty Hawk, North Carolina. In 1914 the first commercial air service began in Florida. Commercial flights began to be flown throughout the United States, Europe, and the rest of the world. As technology improved, longer flights became possible. American aviator Charles Lindbergh’s solo crossing of the Atlantic Ocean in 1927 helped spark public interest in air travel between continents.
    Advances in technology produced faster, larger, and more durable airplanes. The introduction of the turbojet (涡轮喷气飞机) engine in 1941 helped launch the jet age in world travel in the years after World War Ⅱ (1939-1945). The first commercial jet flight in the United States, made by a Boeing 707, occurred in 1958. To handle ever-increasing passenger demand, jet aircraft were made bigger and faster. The Boeing 747 jumbo jet, which can carry over 300 passengers, entered service in 1970. The supersonic (超音波的) British-French Concorde began passenger service in 1972. A helicopter obtains lift from a set of rotor blades (动叶片) rather than from fixed wings, as does an airplane. Helicopters are sometimes used in cities to carry travelers from suburban or downtown locations to airports. Helicopters are also used to provide medical evacuation, traffic reporting, and access to difficult-to-reach spots, such as ocean oil platforms and mountainous regions. Helicopters are also important military vehicles. Military forces use them for cargo transport, for medical evacuation, and as gun ships. The first successful helicopter liftoff occurred in 1907, when a French helicopter left the ground for a few seconds. However, more refinements were needed before helicopters became practical. Germany produced the first practical helicopter in 1936, and the United States Army brought forth its wartime helicopter in 1942. Helicopters were first used for military purposes during World War Ⅱ.
Helicopters were first used for military services in ______.
选项
答案Word War Ⅱ
解析 答案在文章最后一句话“Helicopters were first used for military purposes during World War Ⅱ”，意为“在二战中直升飞机首次用于军事用途”。
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