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Researchers say current exercise guidelines are unrealistic and argue that doctors should sometimes advise small increases in activity instead. They warn the 150-minute weekly target is beyond the reach of some people — particularly older individuals. And striving to reach these goals could mean the benefits of lighter exercise are overlooked. But public health officials say current recommendations have proven benefits in lowering the risk of heart disease.

There is increasing evidence that inactivity is linked to heart disease, Type 2 diabetes(糖尿病) and some types of cancer. UK guidelines for adults recommend at least two-and-a-half hours of moderate activity a week, in short periods of 10 minutes or more.

But in two separate articles in the BMJ, experts argue the message needs to change, with greater emphasis on making inactive people move more. Prof Philipe de Souto Barreto at the University Hospital of Toulouse, advises people who are sedentary(久坐的) to make small incremental increases in their activity levels — rather than pushing to achieve current goals. He points to previous studies which show even short periods of walking or just 20 minutes of vigorous activity a few times a month can reduce the risk of death, compared to people who do no exercise.

In the second article, Prof Phillip Sparking of the Georgia Institute of Technology, says doctors should tailor their advice — particularly for older patients. He suggests using GP visits for people over 60 to discuss "realistic options" to increase activity — such as getting people to stand up and move during TV commercial breaks.

Prof Kevin Fenton at Public Health England, says: "Everyone needs to be active every day — short periods of 10 or more minutes of physical activity have proven health benefits, but getting 150 minutes or more of moderate activity every week is the amount we need to positively impact on a wide range of health conditions. "This includes reducing the risk of heart disease and type 2 diabetes."

At the beginning of this century, medical scientists made an interesting discovery; we are built not just of flesh and blood but also of time. They were  (1)  to show that we all have “a body clock”  (2)  us, which controls the  (3)  and fall of our body energies,  (4)  us different from one day one to the next.

The   (5)  of “a body clock” should not be too  (6)  since the lives of most living things are controlled  (7)   the 24 hour night-and-day cycle. We feel  (8)  and fall asleep at night and become   (9)  and energetic during the day. If the 24 hour-cycle is  (10)  , most people experience unpleasant  (11)   . For example, people who are not  (12)   to working at night can find that  (13)   of sleep causes them to  (14)  badly at work.

  (15)   the daily cycle of sleeping and  (16)  , we also have other cycles which  (17)  longer than one day. Most of us would   (18)  that we feel good on some days and not so good on  (19)   ; sometimes our ideas seem to flow and at other times, they  (20)  ​do not exist.

A new study has found the amount of antibiotics(抗生素) given to farm animals is expected to increase by two thirds over the next 15 years. Researchers are linking the growing dependence on the drugs to the increasing need for meat, milk and eggs. However, the drugs could quicken the development of antibiotic-resistant infections(感染).Such infections are already a major public, health concern in the United States.

The World Health Organization notes when people stop living in poverty, the first thing they want to do is eat better, rather than earn more money. For most people, that means their diet should contain more meat. With the rapid development of Asia, people there are eating nearly four times as much meat, milk and other milk products as they did 50 years ago.

To meet the need, farmers have put many animals into smaller space. As the animals are crowded together, the easiest way to deal with some of the problems of crowding is to give them antibiotics. It's clear that antibiotics help animals stay healthy in a crowded environment and grow faster. But bacteria can develop resistance to the drugs gradually.

Nowadays, doctors find antibiotics that once worked against the infections no longer work. The bacteria have learned ways to fight against the drugs. The heavy use of antibiotics in animals is responsible for the growth of antibiotic resistance worldwide. In the United States, at least two million people get drug-resistant infections each year and at least 23,000 die from an infection.

Europe has banned the use of antibiotics to increase animal growth. And the United States is hoping to persuade farmers to stop using antibiotics for that purpose.

Monarch butterflies（黑脉金斑蝶）are a common summer sight in the northern United States and Canada . These large orange and black insects（昆虫）brighten parks and gardens as they fly lightly among the flowers . What makes monarchs particularly interesting is that they migrate（迁飞）—all the way to California or Mexico and back . They are thought to be the only insect that does this .

       Every year in the late summer monarchs begin their journey to the south . Those heading for Mexico go first for the Louisiana-Mississippi area , then fly across the Gulf of Mexico into Texas . Once in Mexico , they settle themselves in one of about fifteen places in a mountain forest filled with fir trees . Each place provides a winter home for millions of monarchs . The butterflies are so many that they often cover entire trees . When spring comes , they begin their long journey north . 

The question is often asked whether every butterfly makes the round-trip journey every year . And the answer is no . The average monarch lives about nine months . So one flying north might lay eggs in Louisiana and then die . The eggs of that generation may be found in Kentucky ; the eggs of the next generation may end up in Wisconsin or Michigan . The last generation of the season , about the fourth , will make their way back to Mexico and restart the journey .

       Scientists learn about monarchs’ migration by catching and making marks on the insects . By

recatching a monarch with such a mark and noticing where it came from , the next scientist can get to know things like the butterfly’s age and its routing（路线）.

  These days a green building means more than just the color of the paint. Green building can also refer to environmentally friendly houses, factories, and offices.

    Green building means “reducing the impact (影响) of the building on the land”, Taryn Holowka of the U.S. Green Building Council in Washington, D.C., said.

    According to Holowka, building account for (占了) 65 percent of total U.S. electricity use.

But green building can reduce energy and water use. Also, the building are often located near public transportation such as buses and subways, so that people can drive their cars less. That could be good for the environment, because cars use lots of gas and give off pollution. Green building are often built on developed land, so that the buildings don’t destroy forests.

Marty Dettling is project manger for a building that put these ideas into action . The Solaire has been called the country’s first green high-rise building . According to Dettling, “We’ve reduced our energy use by one-third and our water by 50 percent,”

The Solaire cuts energy in past by using solar power. “On the face of the building we have solar panels which change the sun’s energy into electricity,” Dettling explained.

The solaire also has lights that automatically turn off when people leave the room. In addition, the building has lots of windows, allowing people to use the sun for light during the day. The solaire cuts water reusing it.

Not everyone is eager to move into a green building, however. Some people think that things like solar panels cost more money than more traditional energy sources. Anyhow, Holowka said, “It’s going to be big.”

Dreams can be familiar and strange，fantastical or boring，but some dreams might be connected to the mental processes that help us learn.In a recent study，scientists found a connection between nap-time dreams and better memory in people who were learning a new skill.

In the study,99 college students between the ages of 18 and 30 each spent an hour on a computer，trying to get through a virtual maze (迷宫)．The maze was difficult，and the study participants had to start in a different place each time they tried—making it even more difficult.They were also told to find a particular picture of a tree and remember where it was.

For the first 90 minutes of a five-hour break，half of the participants stayed awake and half were told to take a short nap.Participants who stayed awake were asked to describe their thoughts.Participants who took a nap were asked about their dreams before sleep and after sleep—and they were awakened within a minute of sleep to describe their dreams.

Stickgold，a neuroscientist(神经科学家)，wanted to know what people were dreaming about when their eyes werenˈt moving，during sleep.

Four of the 50 people who slept said their dreams were connected to the maze.Some dreamed about the music that had been playing when they were working；others said they dreamed about seeing people in the maze.When these four people tried the computer maze again，they were able to find the tree faster than before their naps.

Stickgold suggests the dream itself doesnˈt help a person learn—itˈs the other way around.He suspects that the dream was caused by the brain processes associated with learning.

All four of the people who dreamed about the task had done poorly the first time，which makes Stickgold wonder if the dreams show up when a person finds a new task particularly difficult.People who had other dreams，or people who didnˈt take a nap，didnˈt show the same improvement.

On the occasional clear-frost autumn night, I was hiking through the dark forest with my GMO wolf. Yes, my best friend is a genetically modified organism（转基因生物）; deliberate selection has produced the blunt-toothed, small-pawed wonder that walks by my side.

      Our world is changing rapidly. In the last five decades, global population has fully doubled, with 3.7 billion hungry mouths added to our planet. During this same time span, the amount of land suitable for agriculture has increased by only 5%. Miraculously, this did not result in the great global famine（饥荒）one might have predicted.

      How do scientists modify a plant so that it makes more food than its parents did? We could treat each harvest like a litter of wolf pups and select only plants bearing the fattest, richest seeds for the next season. This was the method our ancestors used to engineer rice, corn and wheat from the wild grasses they encountered.

      During my childhood, advances in genetic technologies allowed scientists to identify and clone the genes responsible for repressing stem growth, leading to shorter, stronger stalks that could bear more seed—the high-yield crops that feed us today. The 21^st century has brought with it a marvelous new set of high-tech tools with which to further quicken the process of artificial selection. Plant geneticists can now directly edit out or edit in sections of DNA using molecular scissors. We can minimize a plant’s weaknesses while adding to its strengths, and we don’t have to wait for seasons to pass to test the result.

      It is the transformative potential of these techniques to quickly supply the next-generation crops required for upcoming climate change that has led me to believe in the safety and function of GMO plants in agricultural products. We need more GMO research to feed the world that we are creating.

      I love the quiet forest that stands between my lab and my home. But I know that as a scientist, I am responsible first to humanity. We must feed, shelter and nurture one another as our first priority, and to do so, we must take advantage of our best technologies, which have always included some type of genetic modification. We must continue as before, nourishing the future as we feed ourselves, and each year plant only the very best of what we have collectively engineered. I keep the faith of my ancestors each night when I walk through the forest to my lab, and my GMO wolf does the same when she guards my way home.