Scientists recently discovered that pictures on cave walls at Creswell Crags are the oldest known in Great Britain. But they didn't find out in the usual way. Archaeologists often date cave art with a process called radiocarbon dating. The technique can measure the age of carbon found in charcoal drawings or painted pictures. Carbon is an element found in many things, including charcoal and even people. But in this case, there was no paint or charcoal to test. People carved the pictures of animals and figures into the rock using stone tools. The scientists had an "aha!" moment when they noticed small rocks stuck to the top of the drawings. The small rocks must have formed after the drawings were made. "It is rare to be able to scientifically date rock art," said Alistair Pike, an archaeological scientist at Britain's University of Bristol. "We were very fortunate that some of the engravings were covered by stalagmites . When a test proved that the stalagmites formed 12,800 years ago, the scientists knew the art underneath them had to be at least that old. And some of the animals shown, like the European bison, are now extinct--another tip-off that the art is quite old. The artists came to Creswell Crags, This place is one of the farthest points north reached by our ancient ancestors during the Ice Age. At that time, much of the North Sea was dry, so people could move about more easily. Some tools and bones found there are 13,000 to 15,000 years old. They show that the travelers hunted horses, reindeer, and arctic hare. Their artwork is similar to art in France and Germany. It tells scientists that the Creswell Crags artists must have had a close connection to peoples several thousand kilometers away-another important clue to understanding how humans spread out across the world. Why do scientists say the art is quite old? A) The art was carved into stone with stone tools. B) The animals carved in the stone are beautiful. C) The cave is one of the farthest points in the world. D) Some pictures were covered by stalagmites more than 10,000 years old.
D
(Question)
Special ships that create clouds by sending seawater into the air could be the cheapest way of dealing with climate change, new research has found. The technique, known as "marine cloud whitening", would create clouds above the Pacific Ocean that would have a cooling effect by reflecting sunlight away from Earth. Nearly 2,000 wind-powered ships would cross the sea, getting seawater and sending it up through tall tubes. " When you send saltwater into the air, you create bigger and whiter clouds, and thus reflect more sunlight back into space," said David Young from the group of the study. The paper by Professor Eric Bickel and Lee Lane looked into the costs of the projects. It found that cloud whitening would reduce the effects of climate change this century for no more than PS5.3 billion. This is only a small part of the PS150 billion that leading nations are considering spending to cut CO2 emissions each year. It is also more than 25 times cheaper than the PS140 billion cost of another project which would copy the cooling effect of volcanoes. The authors also compared the cost benefits that reducing temperatures would have. They found every PS1 spend on other ways would have PS15 of benefits, however every PS1 spent on cloud whitening would bring PS2,000 of benefits. These would include the human costs on health and the influence on other fields. David Young said, "Marine cloud whitening could achieve as much for the planet as CO2cuts would, but with much less cost." But he warned that these techniques shouldn't be considered as a long-period way to deal with climate change. " It's important to note that this technique wouldn't reduce CO2emissions or deal with the causes of global warming, but would cover its effects." he said. Compared to other projects, cloud whitening _ . A) has a greater effect on volcanoes B) will bring more benefits C) will benefit man's health most D) can reduce temperatures in a better way
(Answer)
B
She's not afraid of anything. Snakes? No problem. Walking alone in the dark? Easy. We're not talking about a superhero here -- SM is a 44-year-old mother. And she's fearless because she happens to be missing part of her brain: the amygdala . Shaped like a pair of almonds sitting in the middle of your brain, the amygdala helps control fear and anxiety. A rare condition called Urbach-Wiethe disease left SM without her amygdala, and seems to have completely erased her sense of fear. To try to understand how the amygdala works, a team of researchers made their efforts to scare SM. They showed her horror movies and took her to the Waverly Hills Sanatorium Haunted House in Kentucky. She pushed out one of the monsters and laughed. SM said she didn't like snakes, but at a pet store full of poisonous creatures, she kept asking to touch them. When asked to rate her feelings, SM reported feeling surprised or disgusted, but never fearful. "She tends to approach everything she should be avoiding," says Justin Feinstein of the University of Iowa. This means the amygdala could control deeper urges to approach or avoid danger. Other scientists have a different opinion, though. "I don't believe you can make a general statement about what the amygdala does by a single case study," Elizabeth Phelps said. In 2002, Phelps published a study on a similar patient with amygdala damage who still showed fear. It may sound like fun to be totally fearless, but we get scared for a good reason. "The nature of fear is survival and the amygdala helps us stay alive by avoiding situations, people, or objects that put our life in danger," Feinstein said. SM was once followed in a park after dark by a man with a knife, and she simply walked away. "It is quite remarkable that she is still alive," said Feinstein. Researchers tried their best to frighten SM in order to find _ . A) The function of a particular organ B) SM's reaction of fear and anxiety C) The process of removing amygdale D) A special way to get along with monsters
A