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.
" u: {9 o; e! h- X' G3 @ 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. 0 L2 O1 a; G$ p1 z+ A* k8 x
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) 5 G. L% y2 v2 U& \' [
4 \* z. ?4 K1 T' t9 r 1.A.shown B.been C.appeared D.proved + M8 ]9 N4 s+ ^) o R
2.A.against B.despite C.beyond D.from
4 l# k+ z) j& F( {3.A.send B.land C.take D.carry b' C/ z$ a& [8 x7 @9 l
4.A.travelers B.astronauts C.researchers D.explorers
' J0 H1 g! ~. G/ {& E5.A.that B.so C.as D.sometimes ; ]% g U H. X g
6.A.made B.discovered C.developed D.invented
7 g! ]3 `6 m3 [( ` t* V5 {7.A.in advance B.before C.earlier D.ago
$ T6 A: |5 j5 X6 C- O8.A.round B.contained C.stored D.burned
) \( X* u6 k- [) E( K- D9.A.as B.into C.for D.the
- Z& \5 e" S% a! D+ |; q3 Y10.A.heating B.escaping C.expanding D.conducting
( p! G( L; R* u$ u5 o& Y11.A.in B.at C.by D.through
c! Y$ F* ?$ a12.A.turns B.goes C.faces D.directs 9 G" R1 z; e5 Y* W. ~
13.A.transmitted B.dispersed C.erected D.radiated + c3 L0 b8 @% P8 Y
14.A.attracts B.leads C.pulls D.pushes ' ]% K7 e: ]: m9 Y
15.A.same B.other C.opposite D.wrong 6 n. t+ x; C2 V% B
16.A.that B.when C.if D.although
- E0 d! Y" l8 Y/ K% R17.A.states B.proves C.follows D.breaks
5 r0 @2 @4 l7 e& R' T; }3 d% K18.A.described B.discussed C.considered D.made N$ i! @. A& K$ k" c5 q3 P; h
19.A.like B.as C.with D.for 2 C2 e, Y, t x: v
20.A.no B.an C.another D.the |