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    Sleep, as we know, is important to us because it helps restore tired organs and tissues in our body. But how much sleep do we actually need?

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    For most of us, eight hours seems to be about the right amount. Yet we know that there are a great many people who get along perfectly with less sleep and some who may even need more. A great deal depends on the way we live. But a good general rule to follow is to sleep as long as we have to in order to feel happy and be able to work at our best when we are awake.

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    There are actually different levels of sleep. There is a deep sleep and a shallow sleep. In a shallow sleep our body does not get the same kind of rest as it gets in a deep sleep, so that after eight hours of a shallow sleep we may still feel tired. But a short deep sleep can be very restful.

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    Alexander the Great was able to get a deep sleep whenever he needed it. Once, during the night before an important battle, he remained awake longer than anyone else. Then he wrapped himself in a cloak and lay down on the earth. He slept so deeply that his generals had to wake him three times to give command to attack!

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    Normally when we go to sleep, our “ sleep center” blocks off nerves so that both our brain and our body go to sleep. One prevents us form wanting to do anything and the other makes our internal organs and limbs go to sleep. But someone will fall asleep (brain sleep) and keep on marching, because his body is not asleep!

    Homework is a major part of going to school: It's your teachers' way of evaluating(评价)how much you understand of what's going on in class. {#blank#}1{#/blank#}Luckily, you can do a few things to make homework less work.

    Be sure you understand the homework.

    Write your homework down in your notebook or day planner if you need to. {#blank#}2{#/blank#}It's much easier to take a minute to ask the teacher during or after class than to struggle to remember later that night!

    Use any extra time in school.

    Many schools have study halls that are specifically designed to allow students to study. It's tempting(诱惑)to hang out with friends during study periods or unstructured(松散的) time. {#blank#}3{#/blank#}

    Take a break.

    {#blank#}4{#/blank#}So take some breaks while doing your homework. Sitting for too long without stretching or relaxing will make you less productive than if you stop every so often. Taking a 15minute break every hour is a good idea for most people.

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    If you don't finish your homework during school, think about how much you have left and what else is going on that day, and then budget your time. Most highschool students have between 1 and 3 hours of homework a night. If it's a heavy homework day and it seems like you've got an assignment in every subject but gym and lunch, you'll need to devote more time to homework. It's a good idea to come up with some kind of homework schedule（日程）, especially if you are involved in sports or activities or have an afterschool job.

A.Pace yourself.

B.Settle down to do homework.

C.And it helps digest important concepts(概念).

D.Most people's attention spans(注意力持续时间)aren't very long.

E.Don't be afraid to ask questions about what's expected.

F.Once your homework is done, you can check over it if you have extra time.

G.But the more work you can get done in school, the less you'll have to do that night.

    Cold weather during winter months may keep many people from leaving home and running in the open air.

    However, a new study shows that the drop in temperature is a good reason to run. In fact, researchers say, running in cold weather helps improve one's performance.

    Many people say running in the winter can be difficult. Two reasons are the low temperatures and bitter winds. Yet many runners might find it easier than running in hot weather.

    That could be because lower temperatures reduce stress on the body. When you run in cold weather, your heart rate and the body's dehydration (脱水) levels are lower than in warmer conditions. The body needs less water on a cold day than in warm weather.

    This information comes from sports scientists at St. Mary's University in London. John Brewer is a professor of applied sport science at St. Mary's.

    For this study, he and other researchers put a group of people into a room they called an “environmental chamber.” The researchers then recreated summer and winter weather conditions in the room. The test subjects were asked to run 10,000 meters under both conditions. Brewer says he and his team recorded biological measurements of the runners.

    “We've got a group of subjects into the environmental chamber, we've changed the conditions to replicate the summer or winter and we've got them to run a 10km under both of those conditions and taken various measurements on each runner while they've been completing their 10km.”

    Brewer says every movement runners make produces heat. He explains that one way in which we lose heat is by sweating. The body loses heat through droplets of sweat. He says the body also loses heat by transporting the blood to the surface of the skin.

    My elephant adventures began in 1984 when, with our one-year-old daughter, my husband and I crossed the jungle in a jeep, slicking behind a lorry for comfort and company. The elephants standing like watchers on either side of the forest highway had us praying for our safety. One elephant made loud noise and angrily pawed (抓) the ground, warning us off. We raced away before they could attack.

    It was wise to keep elephants at a distance. We heard stories of tourists whose jeeps were overturned, and a couple of photographers were killed because they moved too close. Elephants are misleading animals. They give people an impression of being quiet and kind, so tourists think it's safe to picnic in the jungle (丛林). Yet angry elephants have knocked them down in seconds before they could take off.

    Elephants might make life unpredictable and dangerous. It's difficult for inexperienced environmentalists to even, begin to grasp this reality. I've heard city people say " We humans are encroaching (侵害) on their forests." But what's the solution?

    When a poor farmer borrows heavily to plant a crop, he'll do anything to protect it His life depends on it Elephants ruining an about-to-be-harvested corn field cannot expect to be welcomed like special guests. The battle between beast and farmer is violent.

    Experts are working on solutions to human-elephant conflicts (冲突). Some are sure to fail to like the plans to build electric fences around human settlements. Elephants rapidly figure them out and come in, around and over them.

    There are more questions than answers, for sure. But as my husband said, "More people die in car accidents every single day, in every city on the earth. But they won't take cars off the roads, will they?" So we need to seek practical ways of preventing elephant accidents.

    A new officer with the Huntington Park Police patrols (巡逻) local parks 24 hours a day seven days a week. He doesn't need rest, coffee breaks, a salary or medical insurance, and that is because it is a Robocop.

    The main function of the Robocop is to scan and film the surroundings. Besides cameras with night vision that report 360 degrees, it also has a distress button which is located here, so if somebody is to need assistance or they want to contact the communication center, they can do it by way of that distress button. There are people that are monitoring on the other end.

    This newest police employee is self-charging. It's easy to program it and make changes to the software if necessary. Its maintenance (维护) costs are roughly 75 thousand dollars a year. It travels the entire park. It is a programmed path, but the police are able to change the path and adapt it.

    The Robocop can record the license plates (车牌) of passing cars and check them against an online database of stolen cars. It can also help locate a lost iPhone because it is able to determine a smartphone's MAC address. The police can see from the robot if something wrong happens and then come and figure it out.

    The Robocop can't replace its human handlers. The whole goal is to give police more time to do things machines can't do. The police have been having some concerns about safety of the parks and want an extra set of eyes that will help patrol a 24/7.Robocop's creators believe this model known as K5 is best used for providing security at public places like hospitals, parking lots, parks and airports. So far, it seems to be working out just fine.

    I first began experiencing depression (抑郁) at the age of 14 .At first depression would come and go, but later it became a continual part of my life.

    I was so strongly determined to find the way to overcome my depression that I tried everything from when I was in college, special teas, yoga (瑜伽), and advice given by doctors. However, I still felt I hadn't even come close to managing the problem.

    But one afternoon, I saw an article in a magazine that talked about how dogs were able to help people with depression. The next day, I decided to get a dog—a corgi (柯基犬).

    When I bought my little corgi, Buddy, home, I didn't realize how much he would change my life. One morning, I woke up with those familiar feelings again. I didn't want to get out of bed. I turned to pull the covers back over my head and give up. That's when I saw Buddy. He started jumping all over me, licking (舔) my face, letting me know that it was time to go outside. It was as if he were saying, "There's no time to be sad. The world is amazing!" And for the first time in my life, on a day when my depression were strong, I got out of bed. I put on my winter clothes and went for a walk in the snow with my new friend. I realized at that moment, walking down the street in winter, my life was changing. I really was a new person. This was my new beginning.

    It's been more than a year since that day, and I've never spent another morning unable to get out of bed. I've not cried myself to sleep or spent my days filled with fear and regret. Sure, I still have days when I feel sad or anxious. But with Buddy by my side, I've finally learned how to manage these feelings.