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  3. The rocket engine, with its steady roar like that of a waterfall or a thunderstorm, is an impressive symbol of the new space age

The rocket engine, with its steady roar like that of a waterfall or a thunderstorm, is an impressive symbol of the new space age

admin2011-02-28  78
问题    The rocket engine, with its steady roar like that of a waterfall or a thunderstorm, is an impressive symbol of the new space age. Rocket engines have【C1】______powerful enough to shoot astronauts【C2】______the earth’s gravitational pull and【C3】______them on the moon. We have now become【C4】______in space. Impressive and complex【C5】______it may appear, the rocket, which was【C6】______in China over 800 years【C7】______, is a relatively simple device. Fuel that is【C8】______in the rocket engine changes【C9】______gas. The hot and rapidly【C10】______gas must escape, but it can do so only【C11】______an opening that【C12】______backward. As the gas is【C13】______with great force, it【C14】______the rocket in the【C15】______direction. Like the kick of a gun【C16】______it is fired, it【C17】______the laws of nature【C18】______by Sir Isaac Newton when he discovered that"【C19】______every action, there is【C20】______equal and opposite reaction."
【C7】
选项 A、in advance
B、before
C、earlier
D、ago
答案D
解析 过去式。
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