题目

Directions: For each of them. There are four choices marked A, B, C and D. choose the one that fits best according to the Information given in the passage you have just read. Hot Air Balloons A hot air balloon is made up of 3 main parts: The Envelope The actual fabric balloon which holds the air. The Burner The unit which pushes the heat up into the envelope The Basket Where the passengers and pilot stand     The basis of how the balloon works is that warmer air rises in cooler air. This is because hot air is lighter than cool air as it has less mass per unit of volume. Mass can be defined by the measure of how much matter something contains. The actual balloon has to be large as it takes a large amount of heated air to lift it off the ground.     The burner uses propane gas to heat up the air in the envelope to move the balloon off the ground and into the air. The pilot must keep firing the burner at regular intervals throughout the flight to ensure that the balloon continues to the stable. Naturally, the hot air will not escape from the hot at the very bottom of the envelop as firstly, hot air rises and secondly, the floating power keeps it moving up.     To move the balloon upwards, the pilot opens up the propane value which lets the propane flow to the burner which in turn frees the flame up into the envelope. It works in much the same way as a gas grill: the more you open the valve, the bigger the flame to beat the air and the faster the balloon rises.     The “Parachute Valve” at the very top of the balloon is what is used to bring the balloon down towards the ground. It is a circle of fabric cut out of the top of the envelop which is controlled by a rope which runs down through the middle of the envelope to the basket. If the pilot wants to bring the balloon down, he or she simply pulls on the rope which will open the valve, letting hot air escape, decreasing the inner air temperature. This cooling of air causes the balloon to slow its rise.     The pilot can operate horizontally by changing the vertical position of the balloon because the wind blows in different directions at different altitudes. If the pilot wants to move in a particular direction, he or she simply arises and falls to the appropriate level and rides with the wind. （1） The purpose of this article is to __________. A . explain how hot air balloons work B . illustrate why hot air balloons are useful C . describe hot air balloons' structure D . inform readers about how hot air balloons are made （2） What would happen if the “Parachute Valve” could not be released after it was opened? A . The inside of the balloon would continue to heat up. B . The balloon would climb up more rapidly. C . The self-sealing valve would need to take over the role of the Parachute Valve. D . The balloon would begin to move down more rapidly. （3） Which of the following skills or knowledge would be the most useful to a balloon pilot? A . The ability to sew the panels of fabric together to make a balloon. B . An understanding of how propane gas is manufactured. C . A knowledge of the background of passengers who are travelling in the balloon. D . A knowledge of air currents and wind directions in the area where he is piloting the balloon. 答案： A D D

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