When she decided to give up Facebook ..............

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 droughtstricken 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. 

All the following are mentioned as possible factors in drawing insects to weakened trees EXCEPT .............

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

The word “assessing” in paragraph 2 could best be replaced by ...........

According to paragraph 3, which of the following fields is NOT suitable for a person who does not want to live in a big city?

Rain forests cover less than six percent of the earth’s area, but they have 100,000 kinds of all the kinds of plants on the earth. Threefourths of known kinds of plants and animals call the rain forest their home. Twenty percent of our different kinds of medicine comes from rain forests. The glues on an envelope and in shoes come from tropical plants. Rain forests provide materials for hundreds of other products. Rain forests are also very important to the world’s climate. The Amazon rain forest alone receives about thirty to forty percent of the total rainfall on the earth and products about the same percentage of the world oxygen. Some scientists believe that the decreasing size of rain forests will affect the climate on the earth, making it uncomfortable or even dangerous for life. Saving rain forests is an international problem. One country, or even a few countries, cannot solve the problem alone. The nations of the world must work together to find a solution before it is too late. 

What percent of the earth’s area do rain forests cover?

Surgeons in the early 20 century compared with modern ones ............

According to the passage, the positions and colors of the figures in high-tech animation are determined by ..........

What will happen if a dodder plant starts growing where there are no other plants around?

Why are there white rings on each end of the football?

The word “accelerated” in paragraph 5 is closest in meaning to ______.