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  3. The first hot air balloon was made by two French brothers, Joseph and Etienne de Montgolfier. Both brothers worked in the family

The first hot air balloon was made by two French brothers, Joseph and Etienne de Montgolfier. Both brothers worked in the family

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问题         The first hot air balloon was made by two French brothers, Joseph and Etienne de Montgolfier. Both brothers worked in the family business, which was paper manufacturing. The study of flight interested them, and they soon started experiments in this area.
        Joseph was the first to work on hot air balloons, in 1771. He noticed that, when certain gases were burned, it caused materials to rise. Later, Etienne worked with him. At last, they practised with paper bags. They found that hydrogen gas particularly good for this purpose.
        On 4 June, 1783, they produced a linen and paper balloon in the shape of a sphere about 100 meters in diameter. The balloon had an opening to receive the heated air rising from a fire of burning wool and wet straw on the ground. There were some fireproof materials inside the bag to prevent it catching fire. The balloon rose into the air to a height of 2000 meters, and stayed there for about 10 minutes. The only problem with this experiment was terrible smell from the fire of wool and straw!
        Encouraged by this success, the de Montgolfier brothers made a new balloon for passengers. The brothers put a sheep, a duck and a cockerel in it to test it for safety. On 19 September, 1783, the balloon took off from the King of France’ s palace at Versailles(凡尔赛宫). The flight was a success. The animal travelled over three kilometers before landing in a forest. On 21 November of the same year, the brothers launches another balloon. This time, there were passengers on board, a scientist, Jean Pilate de Rozier, and a nobleman, the Marquis d’ Arlandes. The hot air balloon flew for 25minutes over the city of Paris before landing safely. A new means of transport was bom!
Why did not their first big balloon catch fire?_________________________
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答案Because there were some fireproof materials inside the bag．
解析 根据文章第三段第三句话“There were some fireproof materials inside the bag to prevent it catching fire．”可知，第一个气球没有着火的原因是在袋子里装有防火材料。
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