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.
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
Đáp án A
Thông tin ở câu đầu tiên của bài đọc: Sound moves form its source to the ear by wavelike fluctuations in air pressure, something like the crests and troughs of ocean waves. (Âm thanh di chuyển hình thành nguồn gốc của nó trong tai bởi biến động trong áp suất không khí, một cái gì đó giống như các đỉnh và đáy của sóng biển.)