The rocket engine, with its steady roar like that of a waterfall or a thunderstorm, is an
Impressive and complex【80】it may appear, the rocket, which was【81】in China over 800 years【82】, is a relatively simple device. Fuel that is【83】in the rocket engine changes【84】gas. The hot and rapidly【85】gas must escape, but it can do so only through an opening that faces backward. As the gas is radiated with great force, it pushes the rocket in the opposite direction.
(76)
A.shown
B.been
C.appeared
D.proved
![](https://lstatic.shangxueba.com/sxbcn/h5/images/tips_org.png)