【推荐2】Honey(蜂蜜)from the African forest is not only a kind of natural sugar, it is also delicious. Most people, and many animals, like eating it. However, the only way for them to get that honey is to find a wild bees' nest(巢)and take the honey from it. Often, these nests are high up in trees, and it is difficult to find them. In parts of Africa, though, people and animals looking for honey have a strange and unexpected helper一a little bird called a honey guide.

The honey guide does not actually like honey, but it does like the wax (蜂蜡) in the beehives (蜂房). The little bird cannot reach this wax, which is deep inside the bees’ nest. So, when it finds a suitable nest, it looks for someone to help it. The honey guide gives a loud cry that attracts the attention of both passing animals and people. Once it has their attention, it flies through the forest, waiting from time to time for the curious animal or people as it leads them to the nest. When they finally arrive at the nest, the follower reaches in to get at the delicious honey as the bird patiently waits and watches. Some of the honey, and the wax, always falls to the ground, and this is when the honey guide takes its share.

Scientists do not know why the honey guide likes eating the wax, but it is very determined in its efforts to get it. The birds seem to be able to smell wax from a long distance away. They will quickly arrive whenever a beekeeper is taking honey from his beehives, and will even enter churches when beeswax candles are being lit.

【推荐3】As the world's largest terrestrial carnivore (陆地食肉动物), the polar bear is the king of the great white north.Adult males can measure more than 9 feet in length and weigh between 770 and 1,430 pounds.The polar bear has a strong body while their heads are narrow with small, rounded ears.

Polar bears can be found in northern Canada, Greenland, Norway and Russia, and there have been reports that polar bear tracks have been found as far north as the North Pole.The 5,000,000－square－mile range of the polar bear circles the Arctic and contains pieces of open water where seals are easily caught.

Polar bears live on the annual Arctic sea ice that provides a platform from which they can hunt.They hunt seals on the sea ice by breaking into seal dens in the sea ice.The dens aren't visible from above, but seeing is less important than smelling to polar bears—with their sharp sense of smell, polar bears can sense the breathing holes of seals in their dens beneath the snow and ice.As the southern edge of the Arctic ice cap melts in summer, polar bears are forced to stay on land and spend their summers fasting (禁食), living off body fat stored from hunting in spring and winter.

With about 22,000 polar bears living in the wild, the species is not endangered at the moment, but its future is far from certain.Climate change is causing the disappearance of sea ice from which polar bears hunt seals.Sea ice in the Arctic is melting earlier and forming later each year.People have reached an agreement that controls the hunting of polar bears and directs each nation to protect their habitats, but it does not protect the bears against the biggest man－made threat to their survival:   global warming.If current warming trends continue, scientists believe that polar bears may disappear within 100 years.

【推荐1】Early in the morning of June 29, 1991, Carrier and Morgenstern were watching the field. Although they could see nothing through the thick fog, they kept their camera running.

By 6 a.m. the fog began to lift. A remarkable pair of circles had been flattened. Stalks (主茎) were bent but not broken. Outside the circles the wheat was untouched. Muddy though the field was, there were no footprints or other marks. The circles seemed to have come from nowhere. “I can’t explain it at all,” Mike Carrier said to himself with his eyes wide open.

Carrier is not alone since the early 1980s, more than 2000 circles have appeared in farmer’s fields. Most circles form at night between May and August.

Some believe the circles are caused by deer or some other animals. Others think of UFOs. “The circles are messages given by those who come from outer space,” says Michael Green. “Perhaps they are trying to get in touch with us.”

Pat Delgado has done research on crop circles since 1981. He believes that they are caused by “some form of earth energy.”

Most scientists think that there’s no scientific basis to back up Green’s or Delgado’s theories. Some of them say, “ We think they’re nothing but hoax(骗局).”

In September 1991, Doug Bower and Dave Chorley told newsmen that since 1979 they had made circles throughout southern England to fool people who believed in UFOs.

Since the early 1980s, Dr. Terence Meaden has visited more than1000 circles. Now he thinks he may have the answer. He believes true crop circles are made by vortex(旋风) which can flatten the crop in circular patterns.

Now crop circles are still found in southern England each summer. Are they really the traces of UFOs?