Man has long wanted to fly. He saw birds, envied them and tried to imitate

游客2023-10-11 46

问题    Man has long wanted to fly. He saw birds, envied them and tried to imitate them. Over the ages, countless attempts were made: men constructed wings, fastened them to their arms and legs and jumped off towers and hilltops. These "bird-men" flapped (拍动) their wings for a short space of time and then fell to the ground.
【B1】What was not realized in those early years was that birds have muscles very much stronger, in proportion to their size, than men. Human limbs cannot provide sufficient strength to lift the body off the ground.【B2】The secret of flight did not lie in the making of wings, but in discovering the right kind of power, and how to use it.
   In the 18th century, the invention of the hot-air balloon by the Montgolfier brothers of France was seen as a great step forward,【B3】But balloons and the cigar-shaped airship, which was invented slightly later, did not solve the problem of flying because they had no means of power or control. So the difficulty remained: a true flying machine which was heavier than air and capable of carrying people was still to be invented.【B4】Experiments were carried out in many countries, sometimes with models driven by steam engines, but these were too heavy to be used in an airplane with a pilot. The answer finally came at the beginning of this century with the invention of the internal combustion engine (内燃机)--the kind used in motor cars. Here at last was a powerful, yet comparatively light engine, driven by petrol and capable of being fitted into an airplane.
   In 1903, two Americans, the brothers Wilbur and Orville Wright, flew a powered airplane for the first time. Their success encouraged designers everywhere.【B5】Although there were now newer, different problems, mainly to do with safety and the training of pilots, progress was rapid. These were exciting days and interest was intense. The age of airplane arrived. [br] Experiments were carried out in many countries, sometimes with models driven by steam engines, but these were too heavy to be used in an airplane with a pilot.

选项

答案许多国家做了实验，有时用的是蒸汽机驱动的模型，但是这些模型对于由一个飞行员操作的飞机来说都太重。

解析

转载请注明原文地址:https://tihaiku.com/zcyy/3089852.html

相关试题推荐

随机试题

最新回复(0)

Man has long wanted to fly. He saw birds, envied them and tried to imitate

Samanthaworkedveryhardandput.inalotofovertimehoursbecauseshewanted

Whywasit_____hisworkwasnotasgoodashewantedittobe?A、whatB、whichC