Recently,people in US education have gotten extremely worried because a new report has shown that American students have a math problem.

    The 2015 Program for International Student Assessment（评估）(PISA) shows math scores in the US getting lower and no improvement in science or reading.PISA tests 15-year-olds from different countries and regions in their math,science and reading skills.About 540,000 students from 72 countries and regions took part in the assessment in 2015.

    US scores in reading and science were about the same as three years ago,leaving Americans near the middle of the bigger group.But the situation in math is much more worrying.The US average score was 470,be;ow the OECD（经合组织）test average of 490,meaning the US was No.40 among the 72 countries and areas.It was 12 points lower than in 2012 and 18 points lower than in 2009.So,what is going on with American students' math skills?

    One reason may be that the US does not teach math in enough depth."Students are often good at answering the first part of a problem in the United States,"said Andreas Schleicher,director of education and skills at OECD."But as soon as students have to go deeper and answer the more complicated part of a problem,they have difficulties."In comparison,many high-performing countries and regions in math teach a lot less but focus in much greater depth, especially when you look at East Asia,Japan and Singapore,according to Schleicher.

    Another reason may be the fact that many people in the US are unwilling to travel to foreign countries to learn better teaching practices."One of our biggest challenges in the US is that the teachers are not going out and seeing what high-performing countries do differently,"said Wendy Kopp,who started Teach for America,in a news program.

    In recent decades, social isolation has been recognized as a major risk to our health and long life. It's twice as bad for you as being overweight and nearly as bad as smoking. The rising number of people who say they are affected, across a wide range of ages, is shocking. In reality, you can suffer the ill effects of loneliness even if you are not socially isolated.

Comedian Robin Williams made a striking observation in 2014: "I used to think the worst thing in life was to end up all alone. It's not. The worst thing in life is to end up with people who make you feel all alone." Tracking large groups over time indicates that perceived（感知的）social isolation carries its own risk for morbidity（发病率）and mortality.

    The perception of isolation—from others of being in the social aspect-is not only a cause of unhappiness, it also signals danger. Fish have evolved to swim to the middle of their group when predators（捕食者）approach, mice housed in social isolation show sleep disruptions and reduced slow-wave sleep and prairie voles（田鼠）isolated from their partners then placed in an open field explore their surroundings less and concentrate on avoiding predators.

    These behaviours reflect an increased emphasis on self-preservation in the social aspect. For instance, fish on the edge of a school are more likely to be attacked by predators because they are easier to isolate and prey upon. Such observations reflect a more general principle that perceived social isolation in social animals activates neural（神经系统的）, neuroendocrine（神经内分泌的）and behavioural responses that promote short-term self-preservation. However, these responses bring a cost for long-term health and well-being.

    The range of harmful neural and behavioural effects of perceived isolation documented in adults include increased anxiety, hostility and social withdrawal; fragmented sleep and daytime tiredness; increased vascular resistance and changed gene expression and immunity; decreased impulse control; increased negativity and depressive symptoms; and increased age-related cognitive decline.

    Sadly, to date, attempts to reduce loneliness have met with limited success. A series of randomized controlled trials showed that they had only a small effect. Among the four types of interventions（介入）examined, talking therapy that focused on inappropriate thought processes had the largest impact. Social skills training, social support and increased opportunities for social contact were much less effective.

    “Belittle” was first used by Thomas Jefferson, the third president of the United States.

    Many years ago, Buffon, a French naturalist, wrote some books about natural history. The books were a great success even though some critics did not like them. Some critics said, “Buffon is more of a poet than a scientist.”

    Thomas Jefferson did not like what Buffon had said about the natural wonders of the New World. It seemed to Jefferson that Buffon had spoken of natural wonders in America as if they were unimportant.

    This troubled Thomas Jefferson. He was a naturalist, as well as a farmer, inventor, historian, writer and politician. He had seen the natural wonders of Europe. To him, they were no more important than those of the New World.

    In 1788, Thomas Jefferson wrote about his home state, Virginia. While writing, he thought of its natural beauty and then of the words of Buffon. At that moment, Jefferson created a new word－belittle. He said, “Buffon believes that nature belittles her productions on this side of the Atlantic.”

    Noah Webster, the American word expert, liked this word. He put it in his English language dictionary in 1806, “Belittle－to make somebody or something small, unimportant.”

    Americans had already accepted Jefferson's word and started to use it. In 1797, the Independent Chronicle newspaper used the word to describe a politician the paper supported. “He is an honorable man,” the paper wrote, “so let the opposition try to belittle him as much as they please.

    In 1872, a famous American word expert decided that the time had come to kill this word. He said, “'Belittle' has no chance of becoming English. And as more critical writers of America, like those of Britain, feel no need of it, the sooner it is forgotten, the better.” This expert failed to kill the word. Today, “belittle” is used where the English language is spoken.

    When I was a little girl, I remember that when my dad was repairing something, he would ask me to hold the hammer, so we would have time for a conversation with each other. I never saw my dad drinking or taking a night out. All he did after work was taking care of his family.

    I grew up and left home for college and since then, my dad had been calling me every Sunday morning. And when I bought a house several years later, my dad painted it by himself in the fierce summer heat. All he asked was to talk to him, but I was too busy in those days.

    Four years ago, my dad visited me. He spent many hours putting together a swing for my daughter. He asked me to have a talk with him, but I had to prepare for a trip that weekend.

    One Sunday morning we had a telephone talk as usual. I noticed that my dad had forgotten some things that we discussed lately. I was in a hurry, so our conversation was short. Several hours later that day I received a call. My father was in the hospital. Immediately I bought a plane ticket and on my way I was thinking about all the occasions I missed to have a talk with my dad. By the time I arrived at the hospital, my father had passed away. Now it was he who did not have time for a conversation with me. I realized how little I knew about my dad, his deepest thoughts and his dreams.

    After his death I learned much more about him and even more about myself. All he ever wanted was my time. And now he has all my attention every single day.

    The cost of living in countries like the U.S., Britain, Australia or France has skyrocketed (飞涨) in recent years. However, if you are willing to leave your country and explore life in other areas, there are many countries boasting an extremely cheap and low cost of living. Check out the following countries when planning your next move.

    Ecuador

    Ecuador is similar to the United States in many ways, and as a result has become a popular American getaway. They even use the U.S. dollar for their currency. In this country, it is cheaper to eat out every day than cook for yourself on a budget in the U.S. You can even buy a property for around $50,000 and hire someone to tend to it while you are away.

    Mexico

    Although the country is known for its poverty-ridden streets, there are many wealthier areas that provide every facility you might need. You can live off a mere $700 to $800 a month in Mexico, and this includes rent for a nice place, facilities, food, and any sightseeing.

    Argentina

    Argentina has been a popular tourist destination for many years. It has great restaurants, a rich history, and many places to explore. Not to mention, it is not very expensive to live there. A decent sized home can cost around $139,000, which is relatively cheap in relation to homes in the United States.

    Vietnam

    Vietnam has also become a popular tourist destination in recent years. There are many million dollar luxury homes by the beach, but you can find a modest flat or small home for around $25,000 to $50,000 if you search in the right areas.

    Corals (珊瑚) are often described as undersea forests, but they are declining far more quickly than the Amazon. The coral reefs (礁) are likely to be among the first ecosystems to be wiped out by climate change.

    A temperature rise of just 1 to 2℃ can lead to the death of the algae (海藻) upon which corals depend, draining them of color and making the structure more fragile. These bleaching (脱色) events can be temporary if waters cool, but the more frequent they are and the longer they last, the greater the risk of damage is. But that's exactly what is happening. Bleaching was first observed in 1983. It was seen on a global level in 1998, then 2010, and then from 2015 to 2017. Most available scientific evidence tells us that unless we do something to limit warming to 1.5℃, we will lose 99% of the world's coral reefs in coming decades.

    But there are other threats beyond warming. Off the Philippine island of Palawan, its old reefs have been badly damaged by dirty water from the tourist holiday center, pollution from boats and overfishing. The area ought to be a shelter because it's one of the ocean regions most bearable to climate change. "Even here, we are losing our corals," said David Obura, chair of the Global Specialist Group in the International Union for the Conservation of Nature. "We need to reduce stress from overfishing, coastal development, pollution and tourism."

    "I'm a generation of scientists watching them disappear. It's very depressing," Obura said. "Above 1.5℃, in about 50 years, they will be a treasure of historic movies and pictures, but very little to see in real life. Children born today may be the last generation to see coral reefs in all their glory."