1 . “A beautiful field of flowers can be a rather noisy place. It’s just that we can’t hear the sounds.” Scientists at Tel Aviv University have conducted a six-year experiment, proving that plants make noise in certain stressful situations.

Plants produce a high frequency (频率) clicking sound, and when short of water, or damaged, the clicks become far more regular. They also made different sounds, depending on whether they were thirsty or injured. “Each plant and each type of stress is related to a specific sound,” said Professor Lilach Hadany, who led the research study.

Focusing particularly on tomatoes, wheat and corn, the plants were placed in a soundproof(隔音的)room and recorded by microphones. Some plants were starved of water, others cut, and a control group was left undamaged. The researchers used an algorithm (算法) to separate the noises, suecessfully telling the difference between the sounds depending on whether they were dry or cut. The algorithm did this in a greenhouse setting which included far more surrounding sounds, but it was still able to recognize the particular cries for help of the plants.

On average, the human ear can hear sounds up to around 20kHz, while the sounds produced by plants are in the 40-80kHz region, far beyond our hearing. “The sounds made by plants can’t be heard by humans but can probably be heard by various animals, such as bats, mice and insects,” Hadany tells us. Though this has yet to be proven, it’s possible that these creatures use this information to choose which plants to eat.

A study led by Reda Hassanien of China Agriculural University in Beijing years ago, also proved that plants reacted to sound waves, with some plants greatly increasing their yield. While evidence shows that plants can react to sounds, there’s no evidence today that they can actually hear them.

1. What can we know from the six-year experiment?

A．Plants of different types make the sound of the same frequeney.

B．Plants produce more regular sound in certain stressful situations.

C．Plants make sounds with a much lower frequency when stressed.

D．Plants make the sound of the same frequeney whatever the situation.

2. What is the algorithm used for in the research?

A．To record the sounds.	B．To control the sounds.
C．To produce the sounds.	D．To identify the sounds.

3. What has been proven by scientists according to the passage?

A．Plants can hear each other’s cry for help.

B．Animals can hear the sounds made by plants.

C．Plants can make sounds and respond to sound waves.

D．Animals decide what to eat based on the sounds plants make.

4. Which of the following is the best title of the text?

A．Sounds That We Can’t Hear

B．Beautiful Songs from Plants

C．Plants React to Different Types of Stress

D．Plants Talk, Especially When Stressed