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  3. How do fireworks produce their colors? Chemicals that give off bright, distinct colors when burned provide the spectacular co

How do fireworks produce their colors? Chemicals that give off bright, distinct colors when burned provide the spectacular co

admin2010-06-18  34
问题             How do fireworks produce their colors?
   Chemicals that give off bright, distinct colors when burned provide the spectacular colors associated with fireworks. Charcoal and iron, for instance, burn brilliant orange. Strontium salts produce red and barium nitrate gives off green. Blue is the most difficult color to produce, and chemists are still searching for a compound that produces a true shade of blue.
   Once a manufacturer chooses the colors for a firework, the appropriate chemical powders are compressed into small pellets called stars. These stars are normally packed into a Shell containing gun powder. The shell is then put in a launcher — a close-fitting tube, closed at one end, that has been hammered into the ground. The tube acts like a cannon as the pressure from the exploding gunpowder and expanding gases become trapped behind the shell arid shoot it into the sky.
   Depending on the shell design and amount of stars, the firework display varies. A Roman candle, for example, contains only a few stars and shoots them out one at a time, while an aerial shell contains hundreds of stars — each of which leaves a single trail of brilliant color in the sky. For more information about fireworks, contact the National Council on Fireworks Safety, in Washington, D.C., at www. fireworksafety. Com.
The "stars" described in the passage are______.
选项 A、shells that are put in a launcher
B、heavenly bodies in the sky
C、brilliant colors produced by fireworks
D、compressed chemical powder
答案D
解析
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