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。

    Are you sometimes a little tired and sleepy in the early afternoon? Many people feel this way after lunch. They may think that eating lunch is the cause of the sleepiness. Or, in summer, they may think it is the heat. However, the real reason lies inside their bodies. At that time—about eight hours after you wake up—your body temperature goes down. This is what makes you slow down and feel sleepy. Scientists have tested sleep habits in experiments where there was no night or day. The people in these experiments almost always followed a similar sleeping pattern. They slept for one long period and then for one short period about eight hours later.

    In many parts of the world, people take naps (小睡) in the middle of the day. This is especially true in warmer climates, where the heat makes work difficult in the early afternoon. Researchers are now saying that naps are good for everyone in any climate. A daily nap gives one a more rested body and mind and therefore is good for health in general. In countries where naps are traditional, people often suffer less from problems such as heart disease. Many working people, unfortunately, have no time to take naps. Though doctors may advise taking naps, employers do not allow it! If you do have the chance, however, here are a few tips about making the most of your nap. Remember that the best time to take a nap is about eight hours after you get up. A short sleep too late in the day may only make you feel more tired and sleepy afterward. This can also happen if you sleep for too long. If you do not have enough time, try a short nap—even ten minutes of sleep can be helpful.

    Scientists say we are all born with a knack for mathematics. Every time we scan the cafeteria for a table that will fit all of our friends, we're exercising the ancient estimation center in our brain.

    Stanislas Dehaene was the first researcher to show that this part of the brain exists. In 1989, he met Mr. N who had suffered a serious brain injury. Mr. N couldn't recognize the number 5, or add 2 and 2. But he still knew that there are “about 50 minutes” in an hour. Dehaene drew an important conclusion from his case: there must be two separate mathematical areas in our brains. One area is responsible for the math we learn in school, and the other judges approximate amounts.

    So what does the brain's estimation center do for us? Harvard University researcher Elizabeth Spelke has spent a lot of time posing math problems to preschoolers. When he asks 5-year-olds to solve a problem like 21+30, they can't do it. But he has also asked them questions such as, “Sarah has 21 candles and gets 30 more. John has 34 candles. Who has more candles?” It turns out preschoolers are great at solving questions like that. Before they've learned how to do math with numerals and symbols, their brains' approximation centers are already hard at work.

    After we learn symbolic math, do we still have any use for our inborn math sense? Justin Halberda at Johns Hopkins University gave us an answer in his study. He challenged a group of 14-year-olds with an approximation test: The kids stared at a computer screen and saw groups of yellow and blue dots flash by, too quickly to count. Then they had to say whether there had been more blue dots or yellow dots. The researchers found that most were able to answer correctly when there were 25 yellow dots and 10 blue ones. When the groups were closer in size, 11 yellow dots and 10 blue ones, fewer kids answered correctly.

    The big surprise in this study came when the researcher compared the kids' approximation test scores to their scores on standardized math tests. He found that kids who did better on the flashing dot test had better standardized test scores, and vice versa (反之亦然). It seems that, far from being irrelevant, your math sense might predict your ability at formal math.

    Some of the world's most significant problems never hit headlines. One example comes from agriculture. Food riots（暴动）and hunger make news. But the trend lying behind these matters is rarely talked about. This is the decrease in the growth in production of some of the world's major crops. A new study by the University of Minnesota and McGill University in Montreal looks at where, and how far, this decline is occurring.

    The authors take a vast number of data points for the four most important crops: rice, wheat, corn and soyabeans. They find that on between 24% and 39% of all harvested areas, the improvement inproduction that took place before the 1980s slowed down in the 1990s and 2000s.

    There are two worrying features of the slowdown. One is that it has been particularly sharp in the world's most populous countries, India and China. Their ability to feed themselves has been an important source of relative stability both within the countries and on world food markets. That self-sufficiency (自给自足) cannot be taken for granted if productions continue to slow down.

    Second, production growth has been lower in wheat and rice than in corn and soyabeans. This is problematic because wheat and rice are more important as foods, accounting for around half of all calories consumed. Corn and soyabeans are more important as feed grains. The authors note that "we have preferentially focused our crop improvement efforts on feeding animals and cars rather than on crops that feed people and are the basis of food security in much of the world."

    The report also states the more optimistic findings of another new paper which suggests that the world will not have to dig up a lot more land for farming in order to feed 9 billion people in 2050, as the Food and Agriculture Organisation has argued.

    Instead, it says, thanks to slowing population growth, land currently ploughed（犁）up for crops might be able to revert (回返) to forest or wilderness. This could happen. The trouble is that the prediction assumes continued improvements in productions, which may not actually happen.

    Sports can help us a lot. Taking exercises can make us strong. In collective（集体的）sports like basketball, volleyball or football, we will learn the importance of cooperation(合作). And sports can also help us relax after work or study.

    However, as the saying goes, “there are two sides of everything.” Sometimes we may hurt other players or ourselves if we are not careful enough when participating(参加) in sports activities. What's more, too much or hard practice can be bad for our health.

    Sports can make us healthy both physically and psychologically(心理地). It is also a good way for people to know each other and can improve friendship between people. So long as we are careful enough, sports can do us nothing but good.

    When Johnny, a homeless man, spent his last $20, he wasn't looking at it as an investment — but it's about to pay him huge profits. After he helped a woman who ran out of gas, she returned the favor by raising a lot more on the Internet.

    Kate McClure, 27, was driving to visit a friend when she ran out of gas halfway. “He saw me pull over and knew something was wrong,” she wrote. “He told me to get back in the car and lock the doors. A few minutes later, he came back with a red gas can, using his last 20 dollars to make sure I could get home safe.”

    She couldn't repay him at that time because she had no cash with her. “I have been stopping by his spot for the past few weeks. I repaid him for the gas and gave him some clothes.”

    Kate decided to do more for him, so she started a crowdfunding(众筹) campaign on GoFundMe.com, and it quickly gained far beyond its initial $10,000 goal. When it reached $100,000, the fundraising page was shut down for a time at Johnny's request. Because he didn't want to seem like he was taking advantage of the situation. Finally, Kate said that she restarted it because the public interest had not decreased. She also added that Johnny planned to donate the rest to a good cause.

    According to the New York Post  Johnny wants to get a job at an Amazon warehouse and a department manager from the tech company has already reached out, saying he wants to help Jonny.

    We talk continuously about how to make children more "resilient(有恢复力的)", but whatever were doing, it's not working. Rates of anxiety disorders and depression are rising rapidly among teenagers. What are we doing wrong?

    Nassim Taleb invented the word "antifragile" and used it to describe a small but very important class of systems that gain from shocks, challenges, and disorder. The immune system is one of them: it requires exposure to certain kinds of bacteria and potential allergens(过敏源)in childhood in order to develop to its full ability.

    Children's social and emotional abilities are as antifragile as their immune systems. If we overprotect kids and keep them "safe" from unpleasant social situations and negative emotions we deprive(剥夺)them of the challenges and opportunities for skill-building they need to grow strong. Such children are likely to suffer more when exposed later to other unpleasant but ordinary life events, such as teasing and social rejection.

    It's not the kids fault. In the UK, as in the US, parents became much more fearful in the 1980s and 1990s as cable TV and later the Internet exposed everyone, more and more, to those rare occurrences of crimes and accidents that now occur less and less, Outdoor play and independent mobility went down; screen time and adult-monitored activities went up.

    Yet free play in which kids work out their own rules of engagement, take small risks, and learn to master small dangers turns out to be vital for the development of adult social and even physical competence, Depriving them of free play prevents their social-emotional growth. Norwegian play researchers Ellen Sandseter and Leif Kennair warned: "We may observe an increased anxiety or mental disorders in society if children are forbidden from participating in age adequate risky play."

    They wrote those words in 2011. Over the following few years, their prediction came true. Kids born after 1994 are suffering from much higher rates of anxiety disorders and depression than the previous generation did. Besides, there is also a rise in the rate at which teenage girls are admitted to hospital for deliberately harming themselves.

    What can we do to change these trends? How can we raise kids strong enough to handle the ordinary and extraordinary challenges of life? We can't guarantee that giving primary school children more independence today will bring down the rate of teenage suicide tomorrow. The links between childhood overprotection and teenage mental illness are suggestive but not clear-cut. Yet there are good reasons to suspect that by depriving our naturally antifragile kids of the wide range of experiences they need to become strong, we are systematically preventing their growth. We should let go-and let them grow.