Unit 9
If you stand a short distance away from a high wall and shout, your voice sometimes comes back to you as an echo. This happens because the 1 waves are reflected 2 the wall. This is the principle of radar, 3 instead of sound it is radio waves which are reflected. This 4 was made a few years before the last war, 5 radio waves from a transmitting station 6 reflected back from a distant aeroplane.
It was realized 7 an apparatus could be devised to send out radio waves 8 and record the 9 from any approaching aeroplanes, it would be a wonderful method of defense 10 war.
Scientists 11 solving the problem and radar was 12 . An apparatus was made which sent out waves in pulses, and the presence of a distant aeroplane was shown on the screen of a cathode(陰極) ray tube, (this is 13 we have in a television set). 14 this way radar stations could detect the approach of enemy aircraft.
After the war radar was put to peaceful uses. It is now installed at airports to 15 aeroplanes down safely in fog. It is fitted to ships so that they are warned 16 obstructions ahead, 17 icebergs. It guides ships into port. It provides aeroplanes and ships
1. A) voice B) sound C) shout D) echo
2. A) off B) on C) in D) against
3. A) so B) on C) but D) as
4. A) found B) discover C) knowledge D) discovery
5. A) when B) as C) until D) before
6. A) was B) were C) is D) are
7. A) if that B) if when C) that if D) when if
8. A) all time B) every time C) any time D) all the time
9. A) echoes B) voices C) sounds D) waves
10. A) on B) in C) at D) off
11. A) set off B) set aside C) set up D) set about
12. A) found B) seen C) made D) invented
13. A) what B) that C) which D) that
14. A) On B) Upon C) In D) Along
15. A) tell B) guide C) make D) warn
16. A) from B) of C) to D) in
17. A) so on B) so that C) such as D) as if
18. A) with B) of C) for D) in
19. A) which B) that C) this D) what
20. A) away B) along C) off D) far
Nature has a perfect system for recycling water. Water is used again and again. It falls as rain. 1 it goes to one of three places. It might seep slowly through the soil 2 it soaks through into the natural reservoirs 3 . It might disappear into the air by 4 quickly. It might 5 into streams to rivers and to the oceans.
There is a problem 6 this recycling system. It is a balance that can be easily 7 by people. Nature’s recycling system can work well 8 people work with the system—not 9 it. Some ways that people 10 with nature are easy 11 . Dirty sewage water from homes and factories must not 12 with drinking water. People would get sick from drinking dirty water.
13 other ways that people hinder nature. Some of these ways are not so easy to understand. 14 , a marshy bog(沼澤) may not be good for everything, but it 15 an important purpose. The soft, wet soil of a bog 16 water to reach the underground reservoirs. What happens to the balance of nature if the bog is filled in? Many housing development projects have been built 17 marshes once were. The 18 of the houses are likely to have problems. They are likely to 19 water, to flood in 20 seasons. Huge storm sewers are built to carry away with the water from wet areas. These huge pipes prevent wet basements in the houses of the community.
1. A) Therefore B) Then C) Consequently D) Nevertheless
2. A) because B) if C) after D) as
3. A) in underground B) below underground C) underground D) undergroundly
4. A) evaporating B) being evaporating C) having been evaporated D)being evaporated
5. A) run down B) run away C) run off D) run through
6. A) of B) with C) through D) from
7. A) upset B) created C) discovered D) invented
8. A) only before B) unless C) although D) only if
9. A) by B) for C) over D) against
10. A) accord B) concern C) interfere D) interrupt
11. A) to be understood B) understanding C) to understand D)being understood
12. A) separate B) clean C) mix D) filter
13. A) There are B) They are C) These are D) Those are
14. A) To start with B) To name just a few C) For example D) In contrast
15. A) produces B) serves C) maintains D) keeps
16. A) forbids B) discourages C) prevents D) allows
17. A) there B) where C) which D) what
18. A) basis B) base C) basic D) basements
19. A) come up with B) fill up with C) disagree with D) finish with
20. A) dry B) snowy C) rainy D) misty
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