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?

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• What would happen if you pressed the snooze button?

• The word "they" refers to ........

• According to the researchers, husbands should ............

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• Which of the followings is not mentioned as part of the “new media”?

• The word “it” in paragraph 2 refers to ______.

• The word “hazard” in the passage means ................

• The word “harness" in paragraph 4 is closest in meaning to .........

• The word “constituting” is closest in meaning to .........

• The word “captures” in the fourth paragraph is closest in meaning to ______.

• The Asiatic lion ............

• According to paragraph 2, evidence from fossil suggests that ...............

• According to paragraph 1, which of the following is NOT true?

• According to the passage, one function of the memory unit is ...............

• The passage suggests that industrialization in the West led to all of the following EXCEPT .............

• Which of the following can be inferred from the passage?

• Who is intended to benefit from the advice given in the article?

• Pollution in water is noticed .............

• It can be inferred that the names of the three basic shapes mentioned in paragraph 2 reflect ______.

• What killed an estimated 500,000 people in Bangladesh?

• The main idea of this passage is________.