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  3. Why were the Wright brothers able to succeed in an effort at which so many others had failed? Many explanations have been mentio

Why were the Wright brothers able to succeed in an effort at which so many others had failed? Many explanations have been mentio

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问题    Why were the Wright brothers able to succeed in an effort at which so many others had failed? Many explanations have been mentioned, but three reasons are most often cited. First, they were a team. Both men worked congenially and cooperatively, talked incessantly about the possibility of manned flight, and served as a conscious source of inspiration and encouragement to each other.
   Both were glider pilots. Unlike some other engineers who experimented with the theories of flight, they experienced the practical aspects of aerodynamics by building and flying in kites and gliders. They had realized from their experiments that the most serious challenge in manned flight would be stabilizing and maneuvering the aircraft once it was airborne. While others concentrated their efforts on the problem of achieving lift for take-off, they were focusing on developing a three axis control for guiding their aircraft.
   In addition, the Wright brothers had designed more effective wings for the airplane than had been previously engineered. Using a wind tunnel, they tested more than two hundred different wing designs, recording the effects of slight variations in shape on the pressure of air on the wings. The data from theses experiments allowed the Wright brothers to construct a superior wing for their air craft. In spite of these advantages, however, the Wright brothers might not have succeeded had they not been born at precisely the opportune moment in history. Attempts to achieve manned flight in the early nineteenth century were doomed because the steam engines that powered the aircrafts were so heavy in proportion to the power that they produced. But by rite end of the nineteenth century, when the brothers were experimenting with engineering options, a relatively light internal combustion engine had already been invented, and they were able to bring the ratio of weight to power within acceptable limits for flight.
In Paragraph 4, the author suggests that the steam engine used in the earlier aircrafts had failed because ______.
选项 A、they were too small to power a large plane
B、they were too light to generate enough power
C、they. didn’t have internal combustion power
D、they didn’t have enough power to lift their own weight
答案D
解析 由第四段中的第二句“steam engines that powered the aircrafts were so heavy in proportion to the power that they produced”得知：蒸汽机自身的重量和它提供的动力比例失调。
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