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    In America, when the eighth graders leave the middle school, they are often worried about moving to the high school．It is a hard time for them, but it can be an exciting one as well．To make it easier, students need to get familiar with their school.

    Even though they've done this already in the middle school, it's still important to find where their classrooms are．Most schools take students to the high school for a visit at the end of their eighth grade year．And, most schools also have a freshman (新生) speech for parents and students before the first year begins．Sometimes the main office will give away a map of the school．This can help students and parents to find different places in the school.

    One way to know your high school more and make new friends is to join a club or play a sport．Schools often offer chances to join different clubs and sports．Fall activities begin in August before the first day of school．If you are not interested in sports, there are clubs for any interest, such as drama, dance, chess, photography, community service, etc．These clubs allow students from different grades．By joining an activity, students can find new friendships, not to mention improving their chances in future college applications(申请)．The school office will have a list of activities offered at the school and information on how to join them.

    What's more, to have a great start to a high school year, students can write down some of their worries, and ask for help from teachers and school workers.

    Most people know precious gemstones (宝石) by their appearances. An emerald flashes deep green, a ruby seems to hold a red fire inside, and a diamond shines like a star. It's more difficult to tell where the gem was mined, since a diamond from Australia or Arkansas may appear the same to one from the Democratic Republic of the Congo. However, recently, a team of scientists has found a way to identify a gemstone's origin.

    Beneath the surface of a gemstone, on the tiny level of atoms and molecules（分子）, lie clues (线索) to its origin. At this year's meeting of the Geological Society of America in Minneapolis, Catherine McManus reported on a technique that uses lasers (激光) to clarify these clues and identify a stone's homeland. McManus directs scientific research at Materialytics, in Killeen, Texas. The company is developing the technique. “With enough data, we could identify which country, which mining place, even the individual mine a gemstone comes from,” McManus told Science News.

    Some gemstones, including many diamonds, come from war-torn countries. Sales of those “blood minerals” may encourage violent civil wars where innocent people are injured or killed. In an effort to reduce the trade in blood minerals, the U.S. government passed law in July 2010 that requires companies that sell gemstones to determine the origins of their stones.

    To figure out where gemstones come from, McManus and her team focus a powerful laser on a small sample of the gemstone. The technique is called laser-induced breakdown spectroscopy. Just as heat can turn ice into water or water into steam, energy from the laser changes the state of matter of the stone. The laser changes a miniscule part of the gemstone into plasma, a gas state of matter in which tiny particles（微粒）called electrons separate from atoms.

    The plasma, which is superhot, produces a light pattern. (The science of analyzing this kind of light pattern is called spectroscopy.) Different elements produce different patterns, but McManus and her team say that gemstones from the same area produce similar patterns. Materialytics has already collected patterns from thousands of gemstones, including more than 200 from diamonds. They can compare the light pattern from an unknown gemstone to patterns they do know and look for a match. The light pattern acts like a signature, telling the researchers the origin of the gemstone.

    In a small test, the laser technique correctly identified the origins of 95 out of every 100 diamonds. For gemstones like emeralds and rubies, the technique proved successful for 98 out of every 100 stones. The scientists need to collect and analyze more samples, including those from war-torn countries, before the tool is ready for commercial use.

    Scientists like Barbara Dutrow, a mineralogist from Louisiana State University in Baton Rouge, find the technique exciting. “This is a basic new tool that could provide a better fingerprint of a material from a particular locality,” she told Science News.

    Nuclear power's danger to health, safety, and even life itself can be summed up in one word: radiation.

    Nuclear radiation has a certain mystery about it, partly because it cannot be detected by human senses. It can't be seen or heard, or touched or tasted, even though it may be all around us. There are other things like that. For example, radio waves are all around us but we can't detect them, sense them, without a radio receiver. Similarly, we can't sense radioactivity without a radiation detector. But unlike common radio waves, nuclear radiation is not harmless to human beings and other living things.

    At very high levels, radiation can kill an animal or human being immediately by killing masses of cells in vital organs. But even the lowest levels can do serious damage. There is no levels of radiation that is completely safe. If the radiation does not hit anything important, the damage may not be serious. This is the case when only a few cells are hit, and if they are killed immediately. Your body will replace the dead cells with healthy ones. But if the few cells are only damaged, and if they reproduce themselves, you may be in trouble. They can grow into cancer. Sometimes this does not show up for many years.

    This is another reason for some of the mystery about nuclear radiation. Serious damage can be done without the victim being aware at the time that damage has occurred. A person can be irradiated(辐射)and feel fine, then die for cancer five, ten, or twenty years later as a result. Or a child can be born weak as a result of radiation absorbed by its grandparents.

    Radiation can hurt us. We must know the truth.

    Most Europeans want small cars. Many Americans prefer large cars. As a result, European automakers produce a large number of economical, light weight cars, while American automakers build bigger, heavier cars.

    The price of gas has much to do with this. The petrol is expensive in Europe, so Europeans naturally prefer cars that will go a long way on a small amount of fuel. There are other reasons. Many European cities have very narrow streets. In these cities a small car is more practical and easier to handle than a large one.

    Some Americans like powerful engines in their cars. They enjoy having wider cars that are comfortable for large families and long trips. They are prepared to pay higher costs to get these advantages. Other Americans, however, have learned to like the small and smart cars. Many visitors to Europe during and after World War I discovered that small cars were fun to drive and easy to park in small spaces. They were delighted to learn how far small cars could go on a few gallons of gasoline.

    In the 1950s many Americans began buying European cars. In 1957, for the first time, the United States imported more cars than it exported. The best seller among these imported cars was a cool-looking but small car from Germany. Americans immediately gave it another name “ the bug”.

    Today, American car buyers have a wider choice. There are big cars for people who want large room, comfort, and power. And there are small cars, mostly imported but some American-made, for people who want easy parking and economical operation.

On Monday, a scientist and doctor Robert Winston is to formally ask a question in congress about what assessments the government has made "for requiring adults riding bicycles in city centres to heave a licence and third-party insurance". The letter below is the entirely imagined response I would like the government to make to him.

Dear Robert,

You ask what assessments we've made for your proposal about obliging cyclists to have licences and insurance. The brief answer is: none. Nor do we have any plans to do so.

Why? Again, the short answer is this: it's a silly and pointless thing to suggest, as evidenced by the fact that practically no countries or territories anywhere in the world require cyclists to be licensed, or to have compulsory insurance.

I suppose it's only fair if I explain why I think it is such a non-issue. It's pretty simple: such a plan would achieve pretty much nothing, while causing significant problems. More widely, any sensible governments will do everything in their power to get more people cycling, not to put pointless obstacles in their way.

Let's just take one example. As I'm sure you know as a doctor, one of the problems facing our nation is that the National Health System is likely to collapse under the caring for an increasingly overweight population. Inactive living is central to this. Even a fairly brief daily bike trip can have miraculous benefits for people's health.

Next, how would such rules even work? Would the licensing and insurance be just for adults, or also children? How would the system even be enforced-would it also require all bikes to be registered with number plates?

Finally, what would you hope to achieve by this? If you believe licensing transport users stops wrongdoing, can I point to you the data showing how a third of drivers admit to using handheld phones while driving, despite the law forbidding it.

So, to summarize：your plan would be to introduce a hugely new administrative scheme that would most likely have limited effect on the behaviour of averagely law-abiding (守法的) transport users who rarely harm others, while putting people off from this beneficial type of transport.

I'm afraid I just don't get it.