英语听力：自然百科 神秘百慕大 bermuda triangle—11

You don't have to move far up shore before the depths are tremendous and to be able to find an individual wreck in depths like that would be extremely difficult even with modern multibeam sonar technology, and certainly, incredibly difficult with a t

英语听力：自然百科 神秘百慕大 bermuda triangle—10

The couple use global-positioning coordinates to close in on the underwater wreck. We're about 3.6 miles away and its directly southeast from this location. A dark shape looms in the water. It's pretty close. It's easy to be fooled by clouds flying o

英语听力：自然百科 神秘百慕大 bermuda triangle—9

It's very hard to tell. We've just hit the water. It's very hard to tell what altitude we're at. We've crashed the airplane at 930 feet. It seems clear that flying into that methane caused enough confusion in the instruments and with Thomas and he en

英语听力：自然百科 神秘百慕大 bermuda triangle—13

I think the part that Lauras talked about that it has the year 48 on it, and the size of this plan and some other things, I think we may have found the DC3 that disappeared in 1948.That is my real hunch. And I really don't see many other options for

英语听力：自然百科 走进西藏 tibet—16

The full entourage of Tibetan monks make the most of the occasion,with music, prayers, and blessings. Hundreds of fresh prayer flags are prepared and added to the pole. The head lama's sacred scarf adds the final touch to the proceedings. But the sig

英语听力：自然百科 大迁徙 Great Migrations—11

It's a grim end to a short life, but many of the surviving calves will face a more terrifying death. In the Mara River, another migration is culminating. Crocodiles have memorized when and where the wildebeests will try to cross. They have gathered i

英语听力：自然百科 走进西藏 tibet—17

The word for burial in Tibetan means giving offerings to the birds, an act of generosity, in line with the concept of compassion for all beings. By doing good deeds, Buddhists believe that they can contribute to the process of enlightenment. So a sky

英语听力：自然百科 走进西藏 tibet—15

Like a giant hotplate. The plateau heats up in the spring and summer. The change in air pressure draws in warm moist air from the Indian Ocean in the south. Thanks to this, over a billion people from India to Burma benefit from the monsoon rain that

英语听力：自然百科 走进西藏 tibet—14

Out on the plateau,new-born chiru are vulnerable to predators, so their mothers must try to hide and protect them. The most recent problem faced by the chiru is the new Tibet-Qinghai railway, which cuts right through their traditional migration route

英语听力：自然百科 北极熊 冰上间谍 Spy_Bear—7

She leaves little behind. Males are still on the lookout for females. For her cub's safety, she heads back to the hills. But as spring continues, lengthening days bring sudden and dramatic change. The highest tides of the year combine with the rising

英语听力：自然百科 北极熊 冰上间谍 Spy_Bear—6

But again, a bear helps with the filming. Sealed with a kiss, the couples whirlwind romance will last three weeks. Out on the frozen sea, a young male has killed a seal. He caught it when it surfaced through a breathing hole in the ice. To film from

英语听力：自然百科 北极熊 冰上间谍 Spy_Bear—5

She's aware of his difficulties and uses her body as a shield. She must stay attentive if her cub is to survive in this harsh Arctic world. Realizing he's exhausted, she digs a hollow to rest him. In the dens like this, she suckles him six times a da

英语听力：自然百科 北极熊 冰上间谍 Spy_Bear—4

But polar bear courtship is never straightforward. She likes to play hard-to-get. It's also a challenge for blizzardcam. She's testing his fitness, making sure he is a good catch. He skills on the slopes show room for improvement. And now, the female

英语听力：自然百科 北极熊 冰上间谍 Spy_Bear—3

She blinks in the sunlight. She spent her confinement in semi-darkness. She checks that the coast is clear and then reveals her secrets. Time for a stretch. She's been cooped up with her cubs since she gave birth three months ago. They learn by examp

英语听力：自然百科 北极熊 冰上间谍 Spy_Bear—2

She pushes the camera down the slope, a tracking shot. As she films, there is no human presence of any kind. She even adjusts the camera to record her own exit. She must get her cub to the sea-ice before it breaks up and thaws, otherwise, they will b

英语听力：自然百科 大迁徙 Great Migrations—18

But there is desperation here for the crocs well. Eat well now, and they may survive leaner times for months even a year. It's easy to forget that death is as vital to the herd as life. The young emerge from this brutal baptism stronger and wiser. Ba

英语听力：自然百科 大迁徙 Great Migrations—17

The merciless yellow crazy ants take a terrible toll. But by sheer force of numbers and the inexorable will of their genes, they prevail. That is the fierce logic of migrations. But what is logical for the many can be madness for the few. At the Mara

英语听力：自然百科 大迁徙 Great Migrations—16

Finally, they can rest. For another five months, they will cling to this winter refuge, entering a sort of waking trance of energy conservation. Until the longer days of spring awaken them again to mate and pass along to the young--their migratory im

英语听力：自然百科 大迁徙 Great Migrations—15

Soon there may be violence as males joust to win female affections. But for now, everyone enjoys a touching reunion. The calf, out of his depth among these goliaths, returns to the mentoring eye of his mother. He may not leave her for another 10 year

英语听力：自然百科 大迁徙 Great Migrations—14

Many will drown in their frenzy to launch their eggs seaward. Most years, only a handful of their offspring survive. But sometimes, if wind and sea and luck are with them, a tidal wave of tiny crablings will return to these shores. There is no way to