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

Xem lời giải

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Đáp án D
Mục đích của bài này là To report on a new invention (Giới thiệu một phát minh mới). Phát minh đó là sử dụng bộ vi xử lý (a microprocessor) để loại bỏ các âm thanh không mong muốn.

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CÂU HỎI HOT CÙNG CHỦ ĐỀ

Câu 1

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

Hummingbirds are small, often brightly colored birds of the family Trochilidae that live exclusively in the Americas. About 12 species are found in North America, but only the ruby-throated hummingbird breeds in eastern North America and is found from Nova Scotia to Florida. The greatest variety and number of species are found in South America. Another hummingbird species is found from southeastern Alaska to northern California. Many hummingbirds are minute. But even the giant hummingbird found in western South America, which is the largest known hummingbird, is only about 8 inches long and weighs about two-thirds of an ounce. The smallest species, the bee hummingbird of Cuba and the Isle of Pines, measures slightly more than 5.5 centimeters and weighs about two grams. Hummingbirds' bodies are compact, with strong muscles. They have wings shaped like blades. Unlike the wings of other birds, hummingbird wings connect to the body only at the shoulder joint, which allows them to fly not only forward but also straight up and down, sideways, and backward. Because of their unusual wings hummingbirds can also hover in front of flowers so they can suck nectar and find insects. The humming- bird's bill, adapted for securing nectar from certain types of flowers, is usually rather long and always slender, and it is curved slightly downward in many species. The hummingbird’s body feathers are sparse and more like scales than feathers. The unique character of the feathers produces brilliant and iridescent colors, resulting from the refraction of light by the feathers. Pigmentation of other feathers also contributes to the unique color and look. Male and female hummingbirds look alike in some species but different in most species; males of most species are extremely colorful. The rate at which a hummingbird beats its wings does not vary, regardless of whether it is flying forward, flying in another direction, or merely hovering. But the rate does vary with the size of the bird - the larger the bird, the lower the rate, ranging from 80 beats per second for the smallest species to 10 times per second for larger species. Researchers have not yet been able to record the speed of the wings of the bee humming-bird but imagine that they beat even faster. Most hummingbirds, especially the smaller species, emit scratchy, twittering, or squeaky sounds. The wings, and sometimes the tail feathers, often produce humming, hissing, or popping sounds, which apparently function much as do the songs of other birds.

According to the passage, where are hummingbirds found?

A. Throughout the world

B. In South America only

C. In North America only

D. In North and South America

Lời giải

Đáp án D
Giải thích: About 12 species are found in North America, but only the rubythroated hummingbird breeds in eastern North America and is found from Nova Scotia to Florida.

Câu 2

What does the author imply about the rate hummingbirds’ wings beat?

A. Although the bee hummingbird is the smallest, its wings don't beat the fastest.

B. The hummingbird's wings beat faster when it is sucking nectar than when it is just flying.

C. The rate is not much different than that of other birds of its size.

D. The speed at which a bee hummingbird’s wings beat is not actually known.

Lời giải

Đáp án D

Theo thông tin xuất hiện ở cuối đoạn 5 “Researchers have not yet been able to record the speed of the wings of the bee humming-bird but imagine that they beat even faster.” (Các nhà nghiên cứu vẫn chưa thể ghi lại tốc độ đập cánh của loài chim ruồi ong nhưng hãy tưởng tượng là chúng đập thậm chí còn nhanh hơn.), ta có suy ra rằng tốc độ đập cánh của chim ruồi ong vẫn chưa được biết rõ.

Câu 3