2. 职称英语
  3. The great advance【C1】______rocket theory 40 years ago showed that liquid-fue

The great advance【C1】______rocket theory 40 years ago showed that liquid-fue

游客2023-12-27  13
问题     The great advance【C1】______rocket theory 40 years ago showed that liquid-fuel rockets were far【C2】______in every respect to the skyrocket with its weak solid fuel, the only kind of rocket then known.【C3】______, during the last decade, large solid-fuel rockets with【C4】______fuels about as powerful as liquid fuels have【C5】______their appearance, and it is a favorite layperson’s question to【C6】______which one is "better". The question is meaningless.【C7】______might as well ask whether a gasoline or a diesel engine is "better". It all【C8】______on the purpose. A liquid-fuel rocket is complicated,【C9】______has the advantage that it can be controlled beautifully. The burning of the rocket engine can be stopped completely; it can be reignited when【C10】______.【C11】______, 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【C12】______in construction,【C13】______hard to build when a really【C14】______size is desired. But once you have a solid-fuel rocket, it is ready for action【C15】______very short notice. A liquid-fuel rocket has to be fueled first and cannot be【C16】______readiness for very long after it has been fueled.【C17】______, once a solid-fuel rocket has been ignited, it will keep burning. It cannot be stopped and reignited【C18】______desired(it could conceivably be stopped and reignited after a pre-calculated time of burning has e-lapsed. and its thrust cannot be varied. Because a solid-fuel rocket can be kept ready for a long time, most military missiles【C19】______solid fuels, but human-piloted spaceflight needs the fine adjustments that can【C20】______be provided by liquid fuels. [br] 【C3】
选项 A、However
B、Therefore
C、But
D、On the contrary
答案 A
解析 前后句意转折，可选However和But，但But后不能加逗号，所以选However。
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