If you can find a tree which has been cut down，you will see many rings，or circles，on the base of the trunk.By learning to read these rings，you can find out about the tree's life.

    The number of rings tells you how old the tree is.Each year，new wood is formed on the outside of the tree.This new wood is light in color when the tree is growing in spring and summer，and dark in winter when the tree is not growing much.So，if you count the rings of dark­or­light colored wood，you can often find out how old the tree is.

    You can also tell which years have been good years and which years have been bad years.When the light­colored rings are very wide，it means that the tree has been growing quickly that year.If the rings are narrow，it has been growing slowly.If the rings on a tree trunk were greatly magnified，you would be able to see why the rings are light­colored when the tree is growing quickly and dark­colored when the tree is growing slowly.The tree trunk is made up of microscopic tubes，like some pipes，carrying water from the soil，through the trunk，and up to the leaves.They are wide and thin­walled when the tree is growing quickly and they are carrying a lot of water.They are narrow and stuck together when the tree is not growing so quickly.

    When a tree is old，the tubes in the centre of the tree don't carry water.The walls of the tubes have become thick with materials which have stuck along them over the years，forming a kind of wood called“heartwood”．This kind of wood is darker in color than the young，growing wood on the outside of the tree.

    You don't very often see whole tree trunks which have been cut across.But once you learn to read a cross section of the wood，you can see much more in wood which has been used to make boxes，houses and other things.

    In most wood，instead of seeing the trunk cut across，you are seeing it cut along its length.Because you don't see the whole tree，you can't tell how old it is.

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     My husband and I had been married nearly twenty-two years when I acquired Stevens-Johnson syndrome, a disorder where my immune（免疫的）system responded to a virus by producing painful blisters. Although my long-term evaluation was good, I, who had been so fiercely independent, rapidly became absolutely helpless.

My husband, Scott, stepped up to the plate, taking care of kids and cooking dinners. He also became my personal caretaker, applying the medicine to all of my blisters because my hands couldn't do the job. Needless to say, I had negative emotions, bouncing from embarrassment to shame caused by total reliance on someone other than myself.

I recovered from my illness, but I couldn't seem to recover from the thought that I loved my husband less than he loved me. This seeming distinction in our love continued to annoy me for the year following my illness.

Then recently Scott and I went on a long bike ride. He's an experienced cyclist; I'm quite the green hand. At one point with a strong headwind and sharp pain building in my tired legs, I really thought I couldn't go any further. Seeing me struggle, Scott pulled in front of me and yelled over his shoulder, “Stay close behind me.” As I followed his steps, I discovered that my legs quit burning and I was able to catch my breath. My husband was pulling me along-again.

     I pray my husband will always be strong and healthy. But if he should ever become the struggling one, whether on a bike ride or with an illness, I trust Ill be ready to call out to him, Stay close behind me--my turn to pull you along.

    We moved to Elmont in 1956. I was 4 years old. Elmont was a wonderful place to grow up. There were lots of kids, great schools and we had a big yard. My father, Nicholas Denaro, believed that grass was not just to look at, but that children were meant to play on it. We played games and badminton there. A white fence separated our backyard from a small wood. My friends and I jumped the fence and entered the woods.

    My father had the most amazing hand. He could fix anything. He gave those amazing hands to his son, my younger brother, Frank, who also became handy around the house. But my father saved his green fingers for me. He grew flowers, tomatoes, strawberries and figs（无花果） and he shared his love of gardening with me.

    Fourteen years ago, I went to a local nursery and bought a fig tree for Dad for Father's Day. My mother, Bridget Denaro, called it the best gift I could have given him. He planted it exactly in the middle of the front yard.

    He loved that tree and enjoyed delicious figs every year, except just after Sandy hit in 2012. He was so disappointed when cold weather just after the super storm froze all the remaining figs.

In 2015, my father died of aspirating pneumonia(呼吸性肺炎) at 97. We sold our family home of 61 years last year. We left behind Dad's tree, full of figs waiting to ripen. We considered taking it with us, but decided that his Father's Day fig tree belonged to Elmont. The new owner generously allowed me to take some branches so that I could have a precious reminder of my much-loved father and the Elmont home.

    The third week of SEAL training means Hell Week. It is on Wednesday of Hell Week that you paddle down to the mud flats（泥滩） and spend the next 15 hours trying to survive the freezing-cold mud, the howling wind and the increasing pressure from the instructors to quit. As the sun began to set that Wednesday evening, my training class, having broken the rules, was ordered into the mud. The mud consumed each man till there was nothing visible but our heads. The instructors told us we could leave the mud if only five men would quit—just five men and we could get out of the extreme cold.

    Looking around the mud flat, it was apparent that some students were about to give up. It was still over eight hours till the sun came up--eight more hours of freezing cold. The chattering teeth and shivering moans (呻吟）of the trainees were so loud that it was hard to hear anything. And then, one voice began to echo (回荡）through the night--one voice raised in song. The song was terribly out of tune, but sung with great enthusiasm. One voice became two, and two became three, and before long everyone in the class was singing. We knew that if one man could rise above the great suffering then others could as well. The instructors threatened us with more time in the mud if we kept up the singing—but the singing went on. And somehow, the mud seemed a little warmer, the wind a little less bitter and the dawn not so far away.

    If I have learned anything in my time traveling the world it is the power of hope. The power of one person, Washington, Lincoln, King, Mandela and even a young girl from Pakistan, Malala, can change the world by giving people hope.

    So, if you want to change the world, start singing when you're up to your neck in mud.

    Astronomers have taken the first ever image of a black hole, which is located in a distant galaxy (星系).The black hole is 500 million trillion km away and was photographed by a network of eight telescopes across the world. It was captured by the Event Horizon Telescope (EHT).

    The announcement was made in Washington, Brussels, Santiago, Shanghai, Taipei and Tokyo. Details have been published today in Astrophysical Journal Letters.

    Prof Heino Falckc, of Radboud University in the Netherlands, who suggested the experiment, told BBC News that the black hole was found in a galaxy called M87. "What we see is larger than the size of our entire Solar System," he said. "It has a mass 6.5 billion times that of the Sun. And it is one of the heaviest black holes that we think exists. It is an absolute monster, the heavyweight champion of black holes in the Universe."

    The image shows an intensely bright "ring of fire", as Prof Falckc describes it, surrounding a perfectly circular dark hole. The bright halo is caused by very heated gas falling into the hole. The light is brighter than all the billions of other stars in the galaxy combined - which is why it can be seen at such distance from Earth. The edge of the dark circle at the center is the point at which the gas enters the black hole, which is an object that has such a large gravitational pull (万有引 力）,not even light can escape.

    "It is remarkable that the image we observe is so similar to that which we get from our theoretical calculations. So far, it looks like Einstein is correct once again." said Dr Ziri Younsi, of University College London -who is part of the EHT cooperation.

    Chinese scientists were involved in the observation through a telescope in Hawaii. They were also highly involved in follow-up data processing and theoretical analysis, said Shen Zhiqiang, head of the Chinese Academy of Sciences' Shanhai Astronomical Observatory and a member of the EHT international team.

    Shanghai and Taipei were selected as two of the cities to hold news conferences, together with Washington, Brussels, Santiago and Tokyo, a recognition of China's contribution.

    "In the fields of astronomy, radio astronomy, and space astrophysics, China has made a significant contribution to this global project," Falcke said.

    (The New York Times, Oct.7) The 2019 Nobel Prize in physiology(生理学) or medicine was jointly awarded to three scientists — William G. Kaelin Jr., Peter J. Ratcliffe and Gregg L. Semenza — for their work on how cells sense and adapt to oxygen availability. The Nobel Assembly announced the prize at the Karolinska Institute in Stockholm on Monday.

    Their work established the genetic mechanisms(机制) that allow cells to respond to changes in oxygen levels. The findings have implications(启示) for treating a variety of diseases.

    Why did they win?

    "Oxygen is the lifeblood of living organisms(生物体)," said Dr. George Daley, dean of Harvard Medical School. "Without oxygen, cells can't survive." But too much or too little oxygen can be deadly. The three researchers tried to answer this question: How do cells regulate their responses?

    The investigators uncovered detailed genetic responses to changing oxygen levels that allow cells in the bodies of humans and other animals to sense and respond to fluctuations(波动), increasing and decreasing how much oxygen they receive.

    Why is the work important?

    The discoveries reveal the cellular mechanisms that control such things as adaptation to high altitudes and how cancer cells manage to hijack(攫取) oxygen. Randall Johnson, a member of the Nobel Assembly, described the work as a "textbook discovery" and said it would be something students would start learning at the most basic levels of biology education.

    "This is a basic aspect of how a cell works, and I think from that standpoint alone it's a very exciting thing." Johnson said.

    The research also has implications for treating various diseases in which oxygen is in short supply — including anemia, heart attacks and strokes — as well as for treatment of cancers that are fed by and seek out oxygen.