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. ! g4 s0 {+ p/ [ N4 w2 N/ {/ P
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.
( R2 D: h3 T+ Z" U3 O: W 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.”(153words) ' s8 |1 }9 j$ {/ K o. N. c3 \6 @+ u
b* H+ ^$ A, y* V 1.A.shown B.been C.appeared D.proved E+ @) E6 [% k8 t z6 u
2.A.against B.despite C.beyond D.from 0 f" X! I4 g( M
3.A.send B.land C.take D.carry
* B9 c; w& p' |* c/ }+ f& k4.A.travelers B.astronauts C.researchers D.explorers
$ ?" E6 U. I1 k$ i7 |" Q$ m' h5.A.that B.so C.as D.sometimes
. F5 o2 G: x0 m$ s( f6.A.made B.discovered C.developed D.invented 1 }8 G5 ?2 b% m& U% P6 c- N! V
7.A.in advance B.before C.earlier D.ago
, Q4 U: ]# [ Y1 u8.A.round B.contained C.stored D.burned
/ m" J! V x! s! [/ S+ ^5 X1 N9.A.as B.into C.for D.the
; U/ s; t/ v2 G7 C+ b3 d10.A.heating B.escaping C.expanding D.conducting
5 j: o) e, J& b% J: n& b% `0 v6 I2 d11.A.in B.at C.by D.through * {1 L. a7 ^0 T# t
12.A.turns B.goes C.faces D.directs
; `: E& w8 C$ t4 @13.A.transmitted B.dispersed C.erected D.radiated " Q, l% Y6 c* _$ s& @! {7 B* s `4 p
14.A.attracts B.leads C.pulls D.pushes
2 L0 Y3 L+ l) z5 t, q15.A.same B.other C.opposite D.wrong
: u0 s2 P. c6 G16.A.that B.when C.if D.although 7 G* V: n4 z9 ?9 C, A: ^( V, y
17.A.states B.proves C.follows D.breaks 5 [3 y& E& d4 M& b
18.A.described B.discussed C.considered D.made ) V5 _0 c1 W- b R6 z3 H+ e& y
19.A.like B.as C.with D.for . q5 f. m9 h4 V
20.A.no B.an C.another D.the |