【推荐2】Have you ever wondered what wild animals do when no one is watching? Scientists have been able to record the “private” moments of wildlife with leading-edge technology. Low-cost, dependable and small modern cameras are of big help.

Cameras placed in hard-to-reach places have taken videos of everything from small desert cats to later snow-loving felines (猫科动物) in the northern Rocky Mountains. These cameras are important tools to learn new information on wildlife.

Some videos help scientists see the effects of climate change. For example, the desert animal javelina (矛牙野猪) and the tree-loving coatimundi (南美浣熊) have been caught on cameras north of their normal home. This could mean global warming is enlarging their living area northward.

Researchers use cameras, along with Global Positioning Systems or GPS. They attach GPS devices to animals living in or around Yellowstone National Park. Then they can record their movements, or migrations (迁移). These cameras can be left in the wild for days, weeks or even months. They can provide information on how many animals are moving over a given period of time.

Putting those cameras in place requires careful planning. Videos recorded by those cameras can show details about animal behavior. However, they have their problems too. Animals such as wolverines (狼獾) and bears sometimes attack them. Scientists do not know if the attacks are the result of anger or interest. Also, the devices have become popular tools to help hunters look for animals. Some people argue that it is unfair to use the cameras that way. Even with such problems, wild cameras are clearly important scientific tools in researching wild animals.

【推荐2】Early people had very little effect on the environment. They lived in very small 'clan'（部落） groups. They collected or killed only enough for the clan's survival. Early clans were nomadic, which means that they did not stay in one place.     1     . The land had time to recover and animals had time to breed （繁殖） before the clan returned for the next season.   

As time went by, these small family clans joined with others to form larger groups for protection.

    2     . Eventually, people tamed（驯养） wild animals such as dogs and horses. People settled around rivers   and fertile plains to share responsibilities and duties. Then, people began to plant crops instead of moving to areas where the plants grew. This development changed the environment.

    3     . Some people were better at performing a particular task than other clan members, so they began to specialize in things they were good at doing. This also meant that they began to exchange their goods for things that others produced.

People began to communicate with distant tribes. Land was cleared for roads. Foreign plants and animals were transported to places where they had not existed before.     4     . So art, dance and music became important ways of expressing feelings and thoughts. This was how many great civilizations started.

Compared to the past, modern civilization has experienced many changes to become the highly developed society that exists today. Populations have increased rapidly. Inventions and technology have made work easier. However, pollution and other serious problems have also resulted from human progress.     5     .

【推荐3】Many of us might not give a second thought to dropping a small piece of litter. After all, if it is so small, it cannot possibly be that harmful, can it? In today’s world, the answer is certainly “Yes, it can! “With the growing use of plastic bags and the rising number of smokers, there is more litter being produced than ever before.

Although cigarette butts are small, they are bad for the environment. Worldwide, about 4. 3 trillion cigarette butts are littered every year. As well as spoiling the beauty of the environment, they contain poisonous chemicals. These find their way into the water supply where they affect water quality and endanger plants and animals. Cigarette butts can take up to 25 years to break down, and the poisonous chemicals add up to a large amount with so many littered. So, if people want to smoke, they should dispose of the butts properly in a rubbish bin.

Plastic bags are another common form of litter that is dangerous to the environment. They are easily blown by wind and float in water, so they can travel long distances. They find their way to rivers, parks, beaches and oceans, killing many birds, mammals, fish, and sea animals each year worldwide. They can last for hundreds of years in the environment. We should not let plastic bags become litter. We should use fewer plastic bags, and reuse and recycle what we have already used.

One way to reduce the use of plastic bags is to charge for them. Shops used to give plastic bags for free. But in some countries, including China, customers are now charged for each bag. Some shops also have a “bag -for-life “ scheme. They sell strong bags that can be reused, and they replaced them for free if the bags ever break.

Waste is a big problem for the environment, so we need to do something. Not littering at all or cleaning up “small waste” saves money spent on coping with litter properly. However, it would be better not to smoke or use plastic bags at all.

【推荐1】Sure, it's good to get along with your teacher because it makes the time you spend in the classroom more pleasant. And yes, it's good to get along with your teacher because, in general, it's smart to learn how to relate to the different kinds of people you'll meet throughout your life.

But really, there's one super-important reason why you should get along with your teacher. When you do, "learning bursts right open," says Evelyn Vuko, a longtime teacher who writes an education column called "Teacher Says" for the Washington Post newspaper.

In fact, kids who get along with their teachers not only learn more, but they're more comfortable asking questions and getting extra help. This makes it easier to understand new material and do your best on tests. When you have this kind of relationship with a teacher, he or she can be someone to turn to with problems, such as problems with learning or school matters, such as bullying (欺凌弱小者). 

As a kid in a primary or middle school, you're at a wonderful period in your life. You're like a sponge (海绵), able to soak up lots of new and exciting information. On top of that, you're able to think about all this information in new ways. Your teacher knows that, and in most cases, is very excited to be the person who's giving you all that material and helping you put it together. Remember, teachers are people, too, and they feel great if you're open to what they're teaching you. That's why they wanted to be teachers in the first place---to teach!

Some kids may be able to learn in any situation, whether they like the teacher or not. But most kids are sensitive (敏感的) to the way they get along with the teacher, and if things aren't going well, they won't learn as well and won't enjoy being in class.

【推荐2】To learn new things, we must sometimes fail. But what's the right amount of failure? New research led by the University of Arizona proposes a mathematical answer to that question.

Educators have long recognized that there is something of a "sweet spot" when it comes to learning. That is, we learn best when we are challenged to grasp something just outside of our existing knowledge. When a challenge is too simple, we don't learn anything new; likewise, we don't expand our knowledge when a challenge is so difficult that we fail entirely or give up.

So where does the sweet spot lie? According to the new study, it's when failure occurs 15% of the time. Put another way, it's when the right answer is given 85%of the time.

Researchers at the University of Arizona came up with the so-called "85% Rule" after conducting a series of machine-learning experiments in which they taught computers simple tasks, such as classifying different patterns into one of two categories.

The computers learned fastest in situations in which the difficulty was such that they responded with 85% accuracy.

"If you have an error rate of 15% or accuracy of 85%, you are always maximizing your rate of learning in these two-choice tasks," said Professor Robert Wilson.

When we think about how humans learn, the 85%Rule would mostly likely apply to perceptual(感知的)learning, in which we gradually learn through experience and examples, Wilson said. Imagine, for instance, a radiologist(放射科医生)learning to tell the difference between images of tumors(肿瘤)and non-tumors.

"You need examples to get better at figuring out there's a tumor in an image, "Wilson said. "If I give really easy examples, you get 100% right all the time and there's nothing left to learn. You're not going to be taking as much from that as a situation where you are struggling a little hit. If I give really hard examples, you'll he 50% correct and still not learning anything new, while if I give you something in between, you can he at this sweet spot where you are getting the most information from each particular example."