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 (61) powerful enough to shoot
astronauts (62) the earth’s gravitational pull and land them
on the moon. We have now become space (63) . Impressive and complex as it may appear, the rocket, which was (64) in China over 800 years ago, is a relatively simple device. Fuel that is (65) in the rocket engine changes (66) gas. The hot and rapidly (67) gas must escape, but it can do so only through an opening that (68) backward. As the gas is (69) with great force, it (70) the rocket in the (71) direction. Like the kick of a gun (72) it is fired, it (73) the laws of nature (74) by Sir Isaac Newton when he di A. shown B. been C. appeared D. proved 我来回答: 提交
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