When my son, Bob, was in the third grade, he saved all his pocket money for over three months to buy Christmas presents. The third Saturday in December, Bob said he had made his list and had twenty dollars in his pocket.

    I drove him to a nearby supermarket. Bob picked up a basket and went in while I waited and watched in the car. It took Bob over 45 minutes to choose his presents. Finally he came to the checkout counter and reached into his pocket for his money. It was not there! There was a hole in his pocket, but no money. Bob stood there holding his basket, tears falling down his face.

    Then a surprising thing happened. A woman came up to Bob and took him in her arms. "You would help me a lot if you let me pay for you," said the woman. "It would be the most wonderful gift you could give me. I only ask that one day you will pass it on. When you grow up, I would like you to find someone you can help. When you help others, I know you will feel as good about it as I do now."

    Bob took the money, dried his tears and ran back to the checkout counter as fast as he could. That year we all enjoyed our gifts almost as much as Bob enjoyed giving them to us.

    I would like to say "thank you" to that very kind woman, and tell her that four years later, Bob went from house to house collecting blankets and clothes for the homeless people in the fire. And I want to promise her that Bob will never forget to keep passing it on.

    Emily and Zach are confused! Their parents told them they could choose between Massachusetts and Arizona for their vacation this summer.

    Emily has always wanted to visit Boston, the capital of Massachusetts. Zach and she both agree that walking along the Freedom Trail would enable them to see Boston's most famous places of historic interest, like the site of the school Ben Franklin attended and the Old State House. If Emily and Zach went to Massachusetts, they could spend a few days at the beaches on Cape Cod. Emily loves body boarding, and Zach is great at body surfing. They both enjoy building sandcastles .

    Zach finds learning about Native Americans wonderful and has always wanted to travel along the Apache Trail in Arizona. This mountain highway passes Native American ruins in Tonto National Forest. Emily is not as interested in traveling along this trail as Zach, but they both would like to visit Phoenix, the capital, and then travel to Grand Canyon National Park and Meteor Crater (陨石坑). Zach learned in science class that Meteor Crater is a hole over 4,000 feet wide and 520 feet deep that was created when a huge object from space fell to Earth. The object went so deep that it has never been found. Zach would really like to try to discover it. But Emily thinks if experienced scientists and researchers cannot find it, Zach might as well not even bother (费工夫) to try.

    The only drawback for Zach and Emily if they choose Arizona would be the heat. It is very hot and dry in this southwestern state. Massachusetts, on the other hand, is in the northeastern United States. Here Zach and Emily and their parents could enjoy mild (温和的) temperatures. Their parents love hot weather, but Zach and Emily do not really like to sweat.

    How will they ever decide to which state they should travel? If only they could take two trips!

    Scientists think that growing garden grass could be the secret to solving our energy needs, and we may soon be able to replace our gasoline with "grassoline".

    The team, including experts from Cardiff University in Wales, has shown that hydrogen can be taken from grass in useful amounts with the help of sunlight and a cheap catalyst(催化剂) —something that speeds up a chemical reaction without being used up.

    It is the first time that this has been shown and it could lead to a sustainable(可持续的) way of making hydrogen, reported Asian News International. This could be an important kind of renewable energy because it is high in energy and it does not give out harmful gases when it is burned.

    Study co-author Michael Bowker said, "This is really a green source of energy. Hydrogen is seen as an important future energy carrier as the world moves from fossil fuels to renewable energy, and our research has shown that even garden grass could be a good way of getting it."

    Cellulose(纤维素), which is a key part of plants and the biopolymer(生物聚合物) found in the largest numbers on the earth, could be a great source of hydrogen.

In its study, the team looked at the possibility of getting hydrogen from cellulose using sunlight and a simple catalyst.

    This is called photocatalysis(光催化作用) and in it, the sunlight starts the catalyst, which then makes cellulose and water into hydrogen. The researchers studied the effectiveness of three metal-based catalysts, of which nickel(镍) especially interested the researchers, as it is a much more common metal than gold and palladium(钯) and it saves more money.

    According to Bowker, producing hydrogen from cellulose using photocatalysis has not been studied in detail. The team's research shows that large amounts of hydrogen can be produced using this method with the help of a bit of sunlight and a cheap catalyst.

    The study shows that it is effective to use real grass taken from a garden. "This is important as it avoids the need to separate and clean up cellulose, which can be both difficult and costly," said Bowker.

    Floating on the surface of the seas of the world are billions of tons of small plants and animals called plankton. Most of these plants and animals are too small for the human eye to see. They move about lazily with the currents, providing a basic food for many larger animals. Plankton has been described as the equivalent (相等的东西) of the grasses that grow on dry land, and the comparison is an appropriate one. In potential food value, however, plankton far outweighs that of land grasses. One scientist has estimated that while grasses of the world produce about 49 billion tons of valuable carbohydrates(碳水化合物) each year, the sea's plankton produces more than twice as much.

    Despite its enormous food potential, little effort was made until recently to farm plankton as we farm grasses on land. Now scientists have at last begun to study this possibility, especially as the sea's resources appear even more important as a means of feeding an expanding world population.

    No one yet has seriously suggested that “planktonburgers” may soon become popular around the world. As a possible farmed supplementary food source, however, plankton is gaining considerable interest among scientists.

    One type of plankton that seems to have great harvest possibilities is a tiny creature called krill(磷虾). Growing to two or three inches long, krill are a major food source for the giant blue whale, the largest animal ever to live on the Earth. Realizing that this whale may grow 100 feet and weigh about 150 tons, it is not surprising that each one swallows more than one ton of krill daily.

    Krill swim about just below the surface in huge schools sometimes wide, mainly in the cold Antarctic. Because of their pink color, they often appear as an entire reddish mass when viewed from a ship or from the air. Krill are very high in food value. If krill can feed such huge creatures as whales, many scientists reason, they must certainly be competitors among possible new food sources for humans.

    Two graduates from Cambridge University in the United Kingdom found themselves about to graduate, yet with loans to pay off. The pair decided to begin a strange, year-long project to battle their debt.

    The men, Ross Harper and Edward Moyse, set up the website BuyMyFace.com last October as a way to get rid of the £50, 000 they shared as student loans. The idea behind the project was to earn money by selling their faces as advertising space every day for a year. Each day, they advertise a different business by painting the brand's name or logo onto their faces and upload the pictures to the homepage of BuyMyFace.com, adding a link to the advertiser's website and including a short piece of text about it. After they paint their faces and publish them on the website, Harper and Moyse go out to highly populated areas such as music festivals and theme parks to maximize their faces' exposure. They hope more people will pay attention to the advertisements on their faces.

    At this time, Harper and Moyse have advertised their faces for over four months without skipping a day and they're more than halfway to their goal. Though they first started charging a minimum of about £1.60 per company, the prices have risen as their popularity increases. For advertising space during the rest of April, they range between £250 and £750. Terri L. Rittenburg, associate professor of marketing at the University of Wyoming, said that she had heard of people tattooing (纹身) logos on themselves before, but this idea is much better. According to her, at first the idea would be new and unusual and attract attention. People are interested in this particular style of advertisement and would like to try what they advertise. But she is unsure how long it would last.

    At least for now, companies that have bought Harper and Moyse's faces have written positive comments on the pair's website. "We had a three percent increase in website traffic on the very day and for two days more afterwards," said one of the companies.

Tunnels are passageways that are built under the ground. They can also be made under a sea or a river. Some tunnels are dug through high mountains.

For hundreds of years, tunnels have been built all over the world. People use these tunnels to travel from one place to another. Some tunnels are used as waterlanes. Coal and gemstones are also brought from under the ground through long tunnels.

In the past, people dug tunnels using picks and shovels. Rocks and soil were loaded into one-wheel barrows and then onto horses and carts. This work was very tiring.

Today, engineers do a lot of planning before they start to build a tunnel. They use computers to check the level of the water and the types of rock under the ground. When they are sure the area is safe, huge machines are used to dig out the soil.

These machines have an enormous cutting wheel at the front. The wheel slowly grinds (磨碎) through the rock and soil to make the tunnel. Soil that is not needed is carried away in large trucks. As the tunnel becomes longer, it is lined with huge pipes so the walls and roof do not callapse.

Long tunnels have powerful lights to help drivers see the road ahead. Water sprinklers (洒水装置) are fitted to help keep people safe if a fire breaks out in the tunnel.

In large cities, tunnels are built under very busy roads. , People can drive through these tunnels. This makes it quicker to travel to different parts of the city.

Some trains have to wind slowly and carefully over steep mountain slopes. But, in places where there are tunnels, trains can travel quickly through the mountain to reach the other side.