A. composing music
B. repairing alarm systems
C. eliminating engine noises
D. intensifying for warning sounds
C
Đáp án C
Thông tin ở đoạn 1: 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.
=> microprocessor (bộ vi xử lý) được dùng để loại bỏ âm thanh
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