What does fizz (气泡) taste like? In Bubbly (多泡的)drinks such as sodas, tiny bubbles give the drink a lift--- and have a distinct taste, In a new study on mice, scientists have connected that fizzy-taste feeling to the ability to taste sourness, such as that of oranges or vinegar.
Scientists first thought the taste of bubbles came from the bubbles bursting on the tongue, but now ate starting to think differently. Charles Zuker, of Columbia University, and his team studied the nervous system of mice to understand how the tongue tastes carbon dioxide, which is the gas that makes up the bubbles.
Animals, including human beings, are able to detect different tastes by using taste buds(味蕾) which pick up tastes in the mouth, and then send them to the brain. In the experiment, different groups of mice were genetically engineered to be missing one of the senses involved in taste. “Genetically engineered” means the researchers were able to turn off the switches for certain senses by changing the genes responsible for taste. The mice in one group could not taste sweet; another, sour; the third, bitter, and the fourth, salt. When the scientists gave carbon dioxide to the mice, the nervous systems of all the mice responded to the gas, except those of the mice that could not taste sour.
This shows that the taste of the bubbles must be sour, and that by turning off the ability of the mice to taste sour, the scientists also turned off their ability to taste carbon dioxide. When they studied the cells that detect sourness, the researchers found a protein attached to the cells that is important to the process of tasting carbon dioxide. When carbon dioxide comes into contact with this protein, the protein knocks off particles called protons. These protons(质子), in turn, travel to the brain, which says ,” Hey! That’s a taste!”
It may seem like a lot of work to get from a can of soda to a taste, but the science of the senses is anything but simple, “  Taste is a challenging system to study,” one researcher says.
【小题1】 What is the most important function of the bubbles?

A．Nervous Systems Understand How the Tongue Tastes.

B．The Process of Taste

C．The taste of Bubbles.

D．Different Animals Detect Different Tastes.

We human beings haven’t been good friends to animals. For thousands of years, we have been polluting the environment, making it hard for animals to live on the planet. We have been killing animals for their fur, feathers or meat, or simply because they are dangerous. As a result, many kinds of animals have disappeared forever. Hundreds more are on the endangered list today.
Should we care about animals? Of course we should. If animals of a certain kind all disappear, they will never come back again. Animals are more than just resources of things we need. Every kind of animal has its place in the balance of nature. Destroying any kind of animal can lead to many problems. For example, when farmers killed large numbers of hawks, the corn and grain that the farmers stored were destroyed by rats and mice. Why?  Because hawks eat rats and mice. With less and less hawks to keep down their numbers, rats and mice multiplied quickly. And if people kill too many birds, more and more insects will eat the crops.
Luckily, we’ve realized that we shouldn’t kill animals any more. And people are working hard to save those animals that would disappear soon. The government also passed laws to protect the endangered animals. In fact, quite a few countries have passed such laws. These laws forbid the killing of any kind of animal on the endangered list. We should try our best to protect and save the endangered animals.
【小题1】The text calls on us to__________.

We found some _______of rice near the hole . The mice may have stored a lot of____in the hole.

A.grain;grain     B.grain;grains     C .grains; grains    D. grains;grain

A breathtaking trick potentially left over from our ancestors might be found in us — the ability to sense oxygen through our skin.
Amphibians, animals such as frogs that can live both on land and in water, have long been known to be capable of breathing through their skin. In fact, the first known lungless frog that breathes only through its skin was discovered recently in the rivers of Borneo.
Now the same oxygen sensors found in frog skins and in the lungs of mammals (哺乳动物) have unexpectedly been discovered in the skin of mice.
“No one had ever looked,” explained Randall Johnson, a biologist researcher.
Mice and frogs are quite distant relatives, so the fact they have these molecules (分子) in common in their skin suggests they might well be found in the skin of other mammals, such as humans.
“We have no reason to think that they are not in the skin of people too,” Johnson said.   These molecules not only detect oxygen, but help increase levels of vital red blood cells, which carry oxygen around the body. Normal mice breathing in air that is 10 percent oxygen—a dangerously low level similar to conditions at the top of Mount Everest, and about half that of air at sea level. However, mice that had the oxygen sensor HIF-1a genetically removed from their skin failed to produce this hormone (荷尔蒙) even after hours of such low oxygen.
These findings, if they hold true in humans, suggest one could raise the level of oxygen circulating inside the body. This could help treat lung diseases and disorders such as anemia (贫血症) without injecting drugs, which make up a multibillion-dollar market, Johnson said.
Athletes also often try to get more oxygen delivered to their muscles in order to improve their performance. They often do this by training at high altitudes or in low-oxygen tents. The new study suggests they might want to expose their skin as well as breathing in low-oxygen air to improve their performance. “It’s hard to say what exactly might be done, however—there’s a lot we don’t know yet,” Johnson explained.
The scientists detailed their findings in the April 18 issue of the journal Cell.
49. Which of the following statements is TRUE according to the passage?
A. Johnson believes that Oxygen sensors also exist in human skin.
B. People have to surf the Internet to read detailed findings.
C. It has been proved that these findings help treat lung diseases.
D. It has long been expected oxygen sensors exist in mice’s skin. 
50. One of the functions of the molecules mentioned above is _______.
A. carrying oxygen around the body                   B. improving athletes’ performance
C. detecting oxygen                                          D. increasing level of oxygen
51. What is Johnson’s attitude to the application of the findings to the athletes’ training?
A. Negative                  B. Doubting                  C. Positive             D. Hesitating
52. The best title of the passage may be _______.
A. Great Findings Benefits Athletes A Lot
B. Frogs And Mice Are Distant Relatives
C. First Known Animal Breathes Through Skin
D. Humans Might Sense Oxygen Through Skin

Let's face it．No one drinks diet soda for the taste．People drink diet soda in the hope that it will help them lose weight or at least keep them from gaining it．Yet it seems to have exactly the opposite effect, according to a new study．
Researchers from the University of Texas said those who drank two or more diet sodas a day had waist size increases that were six times greater than those who didn't drink diet soda．"What we saw was that the more diet sodas a person drank, the more weight they were likely to gain," said Sharon Fowler．
The study was based on data from 474 participants in a large, ongoing research project, where the participants were followed for nearly l0 years．
While the findings are surprising, they also offer some explanations．
Nutrition expert, Melanie Rogers, who works with overweight patients in New York, has found that when patients are switched from regular to diet soda, they don't lose weight at all．"We weren't seeing weight loss necessarily, and that was confusing to us," said Rogers．
So why would diet soda cause weight gain? No one knows for sure yet, but it could be that people think they can eat more if they drink diet soda, and so over-compensate for the missing calories．
A related study found some sweeteners （甜味剂） raised blood sugar levels in some mice．"Data from this and other potential studies suggest that the promotion of diet sodas and artificial sweeteners may be risky," said Helen P．Hazuda, professor at the University of Texas's school of medicine．"They may be free of calories, but not of consequences．"
【小题1】People drink diet soda to _____．