【推荐1】Do you enjoy eating ketchup on your fries? If so, you must like the essential ingredient in the sauces, tomatoes. The tomato originally comes from South America and has been eaten by people there for thousands of years. Today, tomatoes are popular all over the world. However, when they were first introduced, there was quite a bit of controversy and apprehension surrounding them.

Tomatoes were first planted by the Aztecs (阿兹特克人) in Central America. In fact, ancient Aztec writings mention recipes for dishes of tomatoes. Spanish soldiers conquered the Aztecs and brought tomato seeds back with them to Europe. In Europe, these yellowish tomatoes were first called “apples of gold “. For a long time, people in Northern Europe and North America did not eat these “apples of gold”. The tomato plant looked similar to the nightshade plant, a deadly poison, so they were afraid to eat them. German people even thought that if someone ate tomatoes, he or she would change into a werewolf(狼人). But finally, by the mid-1800s people all over the world had accepted the tomato.

However, the tomato was due for more controversy. Do you think the tomato is a fruit or vegetable? Actually the tomato is a fruit. But in America, the tomato is a vegetable by law. Why is the tomato legally a vegetable in America? In the 1800s, there was no import tax in fruit from other countries. At that time, many tomatoes were coming from other countries into America, and American tomatoes farmers became worried about making a living. The government made the tomato a vegetable by law so that non-American tomatoes would be taxed.

Actually, it is easy to tell that the tomatoes is really a fruit. Cut into a tomato and look inside. You can see many seeds in the center, which is one sign of a fruit. In fact, tomatoes are similar to strawberries. Both have seeds inside, and both grow from the flowers of a plant. And both have delicious flesh surrounding the seeds. Tomatoes and strawberries are actually in the same family.

【推荐2】Walk through the Amazon rainforest today and you will find it is steamy, warm, damp and thick. But if you had been around 15,000 years ago, during the last ice age, would it have been the same? For more than 30 years, scientists have been arguing about how rainforests like the Amazon might have reacted to the cold, dry climates of the ice ages, but until now, no one has reached a satisfying answer.

Rainforests like the Amazon are important for mopping up CO₂ from the atmosphere and helping to slow global warming. Currently the trees in the Amazon take in around 500 million tons of CO₂ each year: equal to the total amount of CO₂ giving off in the UK each year. But how will the Amazon react to future climate change? If it gets drier, will it still survive and continue to draw down CO₂ ?

Scientists hope that they will be able to learn in advance how the rainforest will manage in the future by understanding how rainforests reacted to climate change in the past. Unfortunately, getting into the Amazon rainforest and collecting information are very difficult. To study past climate, scientists need to look at fossilized pollen, kept in lake mud. Going back to the last ice age means drilling deep down into lake sediments （沉淀物）which requires specialized equipment and heavy machinery. There are very few roads and paths, or places to land helicopters and aeroplanes. Rivers tend to be the easiest way to enter the forest, but this still leaves vast areas between the rivers completely unsampled（未取样）.So far, only a handful of cores have been drilled that go back to the last ice age and none of them provide enough information to prove how the Amazon rainforest reacts to climate change.

【推荐3】Winter begins in the north on December 22^nd. People and animals have been doing what they always do to prepare for the colder months. Squirrels(松鼠), for example, have been busy gathering nuts from trees. Well, scientists have been busy gathering information about what the squirrels do with the food they collect.

They examined differences between red squirrels and gray squirrels in the American state of Indiana. The scientists wanted to show how these differences could affect the growth of black walnut(黑胡桃) trees. The black walnuts is the nut of choice for both kinds of squirrels. The black walnut tree is also a central part of some hardwood forests.

Rob Swihart of Purdue University did the study with Jake Goheen, a former Purdue student now at the University of New Mexico. The two researches estimate(估计) that several times as many walnuts grow when gathered by gray squirrels as compared to red squirrels. Gray squirrels and red squirrels do not store nuts and seeds in the same way. Gray squirrels bury nuts one at a time in a number of places. But they seldom remember where they buried every nut. So some nuts remain in the ground. Conditions are right for them to develop and grow the following spring. Red squirrels, however, store large groups of nuts above ground. Professor Swihart calls “death traps for seeds”.

Gray squirrels are native to Indiana. But Professor Swihart says their numbers began to decrease as more forests were cut for agriculture. Red squirrels began to spread through the state during the past century.

The researchers say red squirrels are native to forests that stay green all year, unlike walnut trees. They say the cleaning of forest land for agriculture has helped red squirrels invade Indiana. Jake Goheen calls them a sign of an environmental problem more than a cause.

【推荐1】Is there a way to turn back the aging process in people? For centuries, people have been looking for a “fountain of youth.” The idea is that if you find a magical fountain, and drink its water, you will not age.

Researchers in New York did not find an actual fountain of youth, but they may have found a way to turn back the aging process. It appears that the answer may be called the hypothalamus, which is part of your brain. It controls important body activities, including growth, the way we process food and so on. Researchers found that hypothalamus neural stem cells (干细胞) also influence how fast aging takes place.

Dongsheng Cai was the leading researcher in a study on aging in mice. He and his team reported their findings. “when the hypothalamus starts aging, particularly the loss of hypothalamus stem cells, so does the body.” he said.

Using this information, the researchers began trying to activate (激活) the hypothalamus in laboratory mice. The results show that the treatment slowed aging in the animals. “When we injected the hypothalamus stem cells to the middle-aged mice, the mice aged slowly and they could also live longer.”

But these results were just from studying mice in a laboratory. If the mice can live longer, does that mean people could have longer lives? The next step is to see if the anti-aging effects also work in human beings. If so, they say the findings could lead to new ways to help doctors identify and treat age-related health problems.

【推荐2】There are many colors in nature. But do you think that a color has weight? I think you'll say "no". But I'm afraid you are wrong. If you don't believe it, you may do a small experiment.

First, put two objects with the same weight into two boxes. Then cover the boxes. Third, wrap one box with a red piece of paper, the other one with white piece of paper. OK. Now hold the boxes with your hand one by one. It is certain that you will think the red one is a little heavier.

Why do you think so? A scientist found that different colors have different weights in man's mind. That is to say, every color has its own weight in our mind.

The scientist told us that colors also have smell. Can you smell the color? Of course not. Then why did the scientist say so? That is because every color stands for kind of light with a certain wavelength（波长）. It reaches our brain through sense organs.

According to this discovery scientists say that people accept the colors they like, and refuse the colors they hate. So your body and mind will be healthy by using the colors you like. Or you'll be nervous or even get ill. For example, you like blue and hate red. If you stay in a room with red windows, wallpaper and furniture for two hours, you'll feel you have been there for four hours. But if the room is blue, you'll feel you have been there for only an hour. And if a person walks out of a blue room and into a red room, his temperature will rise. That means our body temperature will change with different colors.