It’s a sound you will probably never hear, a sickened tree sending out a distress signal. But a group of scientists has heard the cries, and they think some insects also hear the trees and are drawn to them like vulture to a dying animal. Researchers with the US Department of Agriculture’s Forest Service fastened sensors to the bark of drought-stricken trees clearly heard distress calls. According to one of the scientists, most parched trees transmit their plight in the 50-hertz to 50-kilohertz range. (The unaided human ear can detect no more than 20 kilohertz). Red oak, maple, white pine, and birch all make slightly different sounds in the form of vibrations at the surface of the wood.

The scientists think that the vibrations are created when the water columns inside tubes that run along the length of the tree break, a result of too little water following through them. These fractured columns send out distinctive vibration pattems. Because some insects communicate at ultrasonic frequencies, they may pick up the trees' vibration and attack the weakened trees. Researchers are now running tests with potted trees that have been deprived of water to see if the sound is what attracts the insects. “Water-stressed trees also smell differently from other trees, and they experience thermal changes, so insects could be responding to something other than sound”, one scientist said.

Which of the following is the main topic of the passage?

Câu hỏi liên quan

• According to the text, the most important quality of a teacher is _______.

• In line 1, the author uses the words “human assistance” to mean ............

• With which of the following statements is the author most likely to agree?

ZUNIA12

• The word formulaic is closest in meaning to___________.

• What is the main topic of the passage?

• Where in the passage is the name of Pippin’s hometown mentioned?

• The author’s tone in the passage is best described as .........

• What is the last paragraph mainly about?

• What does the word magni stand for?

• In the process of drying certain kinds of fruits, sulphur fumes help ______.

• It can be inferred from the passage that the author believes that business operated by women are small because ................

• Which of the following conclusions about squirrels is supported by information in the passage?

• The global community considered the smallpox ___________.

• The passage states that one solution to time management problem is to ..............

• Why did John read about aeroplane?

• "It” in the passage refers to_______.

• The story about college life in Amerian movies are not ...............

• The word “glitches” in the third paragraph can be replaced by ...........

• From paragraphs 6 and 7, we can infer that Melissa Maloney ______.

• If you have a desire to travel, when does the writer suggest that you do it?