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 1 powerful enough to shoot astronauts 2 the earth's gravitational pull and 3 them on the moon. We have now become 4 space.
Impressive and complex 5 it may appear, the rocket, which was 6 in China over 800 years 7 , is a relatively simple device. Fuel that is 8 in the rocket engine changes 9 gas. The hot and rapidly 10 gas must escape, but it can do so only 11 an opening that 12 backward. As the gas is 13 with great force, it 14 the rocket in the 15 direction. Like the kick of a gun 16 it is fired, it 17 the laws of nature 18 by Sir Isaac Newton when he discovered that“19 every action, there is 20 equal and opposite reaction.”
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1.【答案】D
【解析】因其后接形容词powerful作表语故应填系词。shown不是系词;been和appeared虽可作系词但与句意不符;而proved可作系词，意为“证明是”，符合句意。
2.【答案】C
【解析】根据意思判断，beyond意为“超出，超过”。
3.【答案】B
【解析】因land on意为“使……着陆”,而send, take和carry表示“把……送到……上去”时,常接介词to,故应选land.
4.【答案】A
【解析】根据意思判断，travelers正确.
5.【答案】C
【解析】原句是表示让步的状语从句，而且是一个
