Have you ever wondered why birds sing? Maybe you thought that they were just happy. After all, you probably sing or whistle(吹口哨) when you are happy.

    Some scientists believe that birds do sing some of time just because they are happy. However, they sing most of the time for a very different reason. Their singing is actually a warning to other birds to stay out of their territory.

    Do you know what a “territory” is? A territory is an area that an animal, usually the male, claims as its own. Only he and his family are welcome there. No other families of the same species(物种) are welcome. Your yard and house are your territory where only your family and friends are welcome. If a stranger should enter your territory and threaten you, you might shout. Probably this would be enough to frighten him away.

    If so, you have actually frightened the stranger away without having to fight him. A bird does the same thing. But he expects an outsider almost any time, especially at nesting(筑巢) season. So he is screaming all the time, whether he can see an outsider or not. This screaming is what we call a bird's song, and it is usually enough to keep an outsider away.

    Birds sing loudest in the spring when they are trying to attract a mate（配偶）and warn others not to enter the territory of theirs.

    You can see that birds have a language all their own. Most of it has something to do with attracting mates and setting up territories.

    I arrived at my mother's home for our Monday family dinner. The smells of food flew over from the kitchen. Mother was pulling out quilt (被子) after quilt from the boxes, proudly showing me their beauties. She was preparing for a quilt show at the Elmhurst Church. When we began to fold and put them back into the boxes, I noticed something at the bottom of one box. I pulled it out. “What is this?” I asked.

    “Oh?” Mom said, “That's Mama's quilt.”

    I spread the quilt. It looked as if a group of school children had pieced it together; irregular designs, childish pictures, a crooked line on the right.

    “Grandmother made this?” I said, surprised. My grandmother was a master at making quilts. This certainly didn't look like any of the quilts she had made.

    “Yes, right before she died. I brought it home with me last year and made some changes, she said. “I'm still working on it. See, this is what I've done so far.”

    I looked at it more closely. She had made straight a crooked line. At the center of the quilt, she had stitched (缝) a piece of cloth with these words: “My mother made many quilts. She didn't get all lines straight. But I think this is beautiful. I want to see it finished. Her last quilt.”

    “Oh, this is so nice, Mom,” I said. It occurred to me that by completing my grandmother's quilt, my mother was honoring her own mother. I realized, too, that I held in my hands a family treasure. It started with the loving hands of one woman, and continued with the loving hands of another.

阅读下列短文，从每题所给的四个选项 （A 、B 、C  和 D ）中，选出最佳选项。

    Christmastime in the city brings forests of trees already cut and waiting to be sold. But some people like to drive to tree farms. Others wait for their trees to come to them. They order one from the pages of a catalog or on the Internet. Some say the easiest thing of all is to buy a man­made tree with Christmas lights already on it. No falling needles to have to clean up.

    The National Christmas Tree Association says 33,000,000 real trees were sold last year, compared to 9,000,000 man­made ones. Man­made trees generally cost more, but they can be reused. Most natural trees are cut up and recycled, but some people buy trees that can be planted.

    Most Christmas trees are now grown on farms instead of in forests. Twenty-one thousand tree farmers in the United States grow Christmas trees on more than 180,000 hectares. Oregon was the leading producer last year.

    Twenty-two percent of people who bought real trees last year chose them at a farm. Two percent of those people cut the trees themselves. The next most popular places were big stores like Walmart and Home Depot. Groups like the Boy Scouts also sell Christmas trees. But some people pay nothing for theirs. They steal it.

    Cornell University in Ithaca, New York, has many pretty evergreens. Some years ago, a university worker found a way to keep them there. A month before Christmas, workers treated them with “pink ugly mix”. It contains water and red food colour. The bright colour starts to disappear after about a month. It can take longer, however. Cornell decided not to use the mix this year, but the idea has spread.

    Music icon Bob Dylan will not attend the Nobel ceremony in December because he has other commitments(承诺), the Swedish Academy said on Wednesday.

    “The Swedish Academy received a personal letter from Bob Dylan yesterday where he explained that he could not make himself available in December …,” it said in a statement.

    “He wishes that he could accept the award personally, but other commitments make it unfortunately impossible. He said that he felt very honored by the Nobel Prize,” it added. The Swedish Academy said it respected Dylan's decision, but that it was “unusual” for a Nobel laureate(获得者) not to come to Stockholm to accept the award in person. Nobel laureates are honored every year on December 10 ─ the death anniversary of the prize's founder Alfred Nobel, a Swedish industrialist，inventor and philanthropist.

Several other literature prize winners have skipped the Nobel ceremony in the past for various reasons —- British writer Doris Lessing because of ill health, British playwright Harold Pinter because he was under treatment in the hospital and Austrian p laywright and novelist Elfriede Jelinek due to social phobia(社交恐惧症).

“We look forward to Bob Dylan's Nobel lecture, which he must carry out — it is the only requirement — within six months starting from December 10,2016,” the academy said.

    Are you preparing for a big test? If so, you may want to go to play some basketball in between hitting the books. Doctors are starting to find more and more information that suggests a connection between exercise and brain development. Judy Cameron, a scientist at Oregon Health and Science University, studies brain development. According to her research, it seems that exercise can make blood vessels, including those in the brain, stronger and more fully developed. Dr. Cameron is sure that this allows people who exercise to think better. As she says, "While we already know that exercise is good for the heart, exercise can actually cause physical changes in the brain."

    The effects of exercise on brain development can even be seen in babies. Babies who do activities that require a lot of movement show greater brain development than babies who are less physically active. Even a little movement can show big results. Margaret Barnes, a scientist, also believes in the importance of exercise. She thinks that many learning disabilities that children have in primary school or high school can result from a lack of movement as babies. Babies need movement that encourages and excites their five senses. They need to set up a connection between motion and memory. In this way, as they get older, children will begin to connect physical activity with higher learning," says Margaret.

    Older people can develop their brains as well. Cornell University studied a group of seniors who have a short-term memory increase of up to 40 percent after exercising just three hours a week. The exercise does not have to be very difficult, but it does have to increase the heart rate. Also, just like the motion for babies, exercise for older people should not be too simple. Learning some new skills or actions, such as with yoga or tai-chi helps to open up memory paths in the brain that may not have been used for a long time. For most people, any type of physical activity that increases the heart rate is helpful. The main aim is to increase the brain's flow of blood. And your brain can benefit from as little as two to three hours of exercise a week.

We are what we eat. That is an old expression, but one worth knowing. A recent look at diets around the world shows that people who eat healthy food—and not too much of it—live longer. But which areas of the world have the best diets？Researchers found that foods in some of the healthiest diets—Mediterranean, New Nordic, Japanese and French—may be very different, but they are all heavy on local, seasonal and limit processed foods, which are high in vegetables and seafood and low in red meat.

Mediterranean diet contains lots of fruits, vegetables, whole grains, nuts and olive oil. The diet has proper amounts of fish and poultry (禽肉). Red meat and foods high in sugar and salt are not big parts of this diet.

New Nordic diet has whole grains like oats and rye, vegetables such as carrots, broccoli and eggs, seafood, fruits, oil, low­fat milk and cheese. Very sugary desserts are not common in this diet.

Japanese people are some of the longest­living people on the planet, with women up to 87 years old and men up to 80. The Japanese diet is the reason for such lengths of life. The diet has many foods that are low in calories and high in nutrients. Japanese people eat a lot of seaweed, tofu, rice, vegetables and fish. The tradition there is to stop eating when your stomach feels 80 percent full.

However, French people eat fatty foods but do not get fat. And they live a long time. This phenomenon is called the "French Paradox". The reason why the French eat fatty foods without getting fat may be simple. They eat less. Serving sizes in French restaurants and in products sold in stores are smaller than those in most countries. And generally speaking, most French people do not snack. This means they do not eat food between meals.