Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to the following questions. 

Sound moves form its source to the ear by wavelike fluctuations in air pressure, something like the crests and troughs of ocean waves. Once way to keep from hearing sound is to use ear plugs. Another way is to cancel out the sound with anti-sound. Using a noisemarker controlled by a microprocessor, engineers have produced sound waves that are half a wavelength out of phase with those of the noise to be quieted-each crest is matched to a trough, and vice versa. Once the researchers have recorded the offending sound, a microprocessor calculates the amplitude and wavelength of sound that will cancel out the crests and troughs of noise. It then produces an electric current that is amplified and fed to a loudspeaker, which produces anti-sound and wipes out the noise. If the anti-sound goes out of synchronization, a microphone picks up the leftover sound and sends it back to the microprocessor, which changes the phase of the anti- sound just enough to cause complete silence.

The research team has concentrated on eliminating low-frequency noise from ship engines, which causes fatigue that can impair the efficiency and alertness of the crew, and may mask the warning sounds of alarm and fog signals. 

What is the main purpose of the passage?

• A. To discuss a physical handicap
• B. To warn about a growing danger
• C. To describe the structure of the ear
• D. To report on a new invention

• Câu 2: Mã câu hỏi: 44761

  The passage compares sound to_________.

  • A. the rising and falling of water in the ocean
  • B. the crests and valleys of mountain ranges
  • C. a flag waving in the air
  • D. a machine for gauging air pressure

• Câu 3: Mã câu hỏi: 44762

  The passage discusses a way to deal with an offensive noise by_________.

  • A. diverting people's attention from it
  • B. masking it with a louder noise
  • C. canceling it out electronically
  • D. removing its source

• Câu 4: Mã câu hỏi: 44763

  The microprocessor described in the passage will probably be used for_________.

  • A. composing music
  • B. repairing alarm systems
  • C. eliminating engine noises
  • D. intensifying for warning sounds

• Câu 5: Mã câu hỏi: 44764

  The researcher mentioned in the passage are concerned about unwanted noise because it can_________.

  • A. cause deafness
  • B. create hazardous working conditions
  • C. influence ocean waves
  • D. damage loudspeakers and sound equipment

• Câu 6: Mã câu hỏi: 44765

  According to the passage, what group of people will probably first from the use of the microprocessor?

  • A. Ship's crews
  • B. Research engineers
  • C. People with insomnia
  • D. Engine repair teams

• Câu 7: Mã câu hỏi: 44766

  A paragraph following the passage would most probably discuss_________.

  • A. the nature of fog
  • B. a way to improve alarm systems
  • C. other causes of fatigue
  • D. other uses for the microprocessor