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[originaltext] The great advance in rocket theory 40 years ago showed that l
[originaltext] The great advance in rocket theory 40 years ago showed that l
游客
2023-08-22
66
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问题
The great advance in rocket theory 40 years ago showed that liquid-fuel rockets were far superior in every respect to the skyrocket with its weak solid fuel, the only kind of rocket then known. However, during the last decade, large solid-fuel rockets with solid fuels about as powerful as liquid fuels have made their appearance, and it is a favorite layman’s question to inquire which one is "better".(16)The question is meaningless; one might as weft" ask whether a gasoline or a diesel engine is "better". It all depends on the purpose.(18)/(19)A liquid fuel rocket is complicated, but has the advantage that it can be controlled beautifully. The burning of the rocket engine can be stopped completely; it can be reignited when desired. In addition, the thrust can be made to vary by adjusting the speed of the fuel pumps. A solid-fuel rocket, on the other hand, is rather simple in construction, though hard to build when a really large size is desired. But once you have a solid-fuel rocket, it is ready for action at very short notice. A liquid-fuel rocket has to be fueled first and cannot be held in readiness for very long after it has been fueled. However, once a solid-fuel rocket has been ignited, it will keep burning. It cannot be stopped and reignited whenever desired(it could conceivably be stopped and reignited after a pre-calculated time of burning has elapsed)and its thrust cannot be varied. Because a solid-fuel rocket can be kept ready for a long time, most military missiles employ solid fuels,(18)but manned spaceflight needs the fine adjustments that can only be provided by liquid fuels.(19)It may be added that a liquid-fuel rocket is an expensive device; a large solid-fuel rocket is, by comparison, cheap.(17)/(19)But the solid fuel, pound per pound, costs about 10 times as much as the liquid fuel.(19)So you have, on the one hand, an expensive rocket with a cheap fuel and on the other hand a comparatively cheap rocket with an expensive fuel.
Questions 16 to 19 are based on the passage you have just heard.
16. What conclusion can we draw from the passage?
17. Why are the solid-fuel rockets expensive to operate?
18. What’s the most important consideration for the rocket that used for manned spaceflight?
19. Which of the following statements is NOT the characteristic of liquid-fuel rockets?
选项
A、The inexpensive cost of construction.
B、The capacity of lifting heavy spacecraft into orbit.
C、The easy control performance.
D、The inexpensive cost of operation.
答案
C
解析
推理题。题目是问用于发射人造航天器的火箭要重点考虑什么。短文中在提到manned spaceflight时说要使用液体燃料火箭,根据前文,比较液体燃料火箭和固体燃料火箭的优缺点时说到,液体燃料火箭的优点是能够被完美地控制,其点火装置可以完全停止,在需要的时候可以重新点火,此外,其助推器可以通过调整燃油泵的速度进行改变。所以液体燃料火箭有易于控制的特点,故选C。
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