4 . To the human ears a field of flowers is silent, save the noise of birds and insects. To certain animal ears, however, a field of flowers is full of conversation.   

It has long been known that plants communicate when stressed. You need only observe a houseplant to realize that a plant wilts (枯萎) when it needs water, or turns yellow at the edges when it has been watered too much. Some plants may also emit a bitter taste to deter insects from capitalizing on their stressed state; while others may emit organic compounds to alarm other plants in the area.

Now, a new study, conducted by researchers at Tel Aviv University. shows that not only do plants express themselves in the above ways when stressed, they also emit sounds.

According to the study, plants emit sounds at frequencies between 40 to 80 kilohertz- beyond the range of human ears—but within the range of some animals. “While imperceptible to the human ears, the sounds emitted by plants can probably be heard by such animals as bats, mice, and insects, "explained Dr. Lilach Hadany, a Professor at Tel Aviv University and a co-author of the study.

One of the primary breakthroughs of Hadany's study is that the researchers have managed to understand and classify the sounds that plants generate for the first time. Plants that are not stressed produce about one noise per hour, but plants that are stressed, dehydrated, or injured many hundreds of sounds per hour, and each of these sounds seems to be specific to the type of stress the plant is under.

This type of information could be vital for agriculture. Knowing what sounds their plants are making could help farmers determine whether their crops are in danger or drought or disease and allow them to make the necessary changes to let their plants to thrive.

Amazingly enough, the researchers are not actually sure how the plants make sounds, though it may have something to do with cavitation (空穴现象), which is when the water tension in the plants becomes too high and the water turns to gas, making an ultrasonic popping noise.

Whatever the case, this is still a game-changer for plant science, and potentially for the future of agriculture. One day soon your plants may be-able to tell you if they are hungry, thirsty, or just feeling lonely.

7 . My name is Maggie and I am a big red maple tree in the center of Central Park in New York. Every part of me is _________ shaped. I love seeing all the people _________, stare at me, and say “That tree is beautiful!” Those _________ make me feel special.

One day, I see a big storm _________ my way. I can hear all the frightening sounds nearing, but the most frightening one is the sound of almost half of my bark being torn off. I feel _________. What will people think when they walk up to a worn-down tree in the middle of Central Park? Will they cut me down? This _________ makes my branches ache.

Hours later, when the storm _________, a nice opossum family comes to me and asks _________ they can spend the night in one of my holes. The baby opossum is so cute that I can’t _________. Soon, round two of the storm comes. It __________ another part of my bark, but it doesn’t __________ me as much because I have a distraction: the opossum family. Other animals see my __________ act and come to me, too. Even though I feel great for __________ all the animals, I still haven’t completely forgotten about what people might think about my __________. Beyond all expectations, people love me even more for protecting all those animals from the terrible storm. This serves as a __________ to me that “beautiful” doesn’t always refer to looks.

Bamboo is called “poor people’s material” and even in China it is not       1     (wide) accepted as a modern building material. But bamboo makes nearly the lightest houses, which       2     (become) better than “modern” materials at surviving earthquakes over the years.

And unlike the “Tofu” buildings that may     3     (destroy) in just several seconds in some earthquakes, bamboo makes a much     4     (safe) building. That is why it is suggested as a replacement(替代品)by International Network for Bamboo and Rattan (INBAR).

INBAR notes that     5     number of people who do not have safe and healthy shelter will increase with population growth if no proper action is taken.

Study shows that bamboo is excellent in     6     (strong) and is as strong as wood. Besides, because     7     the lightweight and good elasticity(弹性)of bamboo, bamboo buildings are very good at resisting(抵抗)earthquakes. For example, all of the 30 bamboo houses survived without any damage in the 7. 6 magnitude earthquake in Costa Rica in 2012.

Ancient Chinese people preferred living in houses     8     (make) of bamboo. In Yunnan Province, some locals still live in bamboo homes which can protect       9    (they) from rain and wind. And in Zhejiang Province,     10    bamboo is plentiful, local officials have been encouraging architects to design buildings using bamboo.

10 . Fallen leaves are everywhere as winter comes. Traditionally, people sweep up the fallen leaves, put them in bags and send them to landfills. But there is a growing movement to leave leaves on the ground. They’ll naturally break down over the winter into rich organic matter. The matter also shelters some insects.

But some leaves prevent the growth of other plants. Black walnut (黑胡桃), for example, contains a poison in its leaves that kills many plants, including apples, peppers, tomatoes and potatoes. Besides, whole leaves should not be permitted to remain on walkways, where they could make the path dangerously slippery. They should also not be left on grass lawns, where they are likely to cause disease. In areas that experience snow cover, water would become trapped between grass and leaves. In areas without snow, whole leaves that cover grasses block water and sunlight from reaching the soil below.

Many people choose to break up the leaves using a machine and let the pieces fall between pieces of grass. Then the pieces break down further in the soil. However, this treatment can kill insects and their eggs.

Another method is to take the leaves off the lawn and spread them lightly to cover garden beds. The leaves mostly break down by spring and almost entirely by summer. But if not, they should be removed before spring growth begins.

Leaves also can be used to make leaf mold (腐叶土), a type of fertilizer made entirely from leaves. Just put the leaves in a corner, add nitrogen fertilizer (氮肥), and then water them to keep them wet inside. It may take a year or two, but the leaves will break down into a nutritious soil.

Fallen leaves build rich soil, protect plant roots and shelter wildlife, in your garden, and elsewhere. Done correctly, leaving the leaves is one of the best ways to turn yard waste into free fertilizer, which is good for plants, the environment, and saving money. Why waste that important resource?