阅读下列短文，从每题所给的四个选项（A、B、C、D）中，选出最佳选项

    You may have heard adults say they are uncomfortable in the morning without a cup of coffee. One reason they may feel that way is that coffee contains caffeine(咖啡因). Caffeine appears naturally in coffee, tea, and cocoa beans, which are used to make chocolate. But now food makers are adding it to many products, from potato chips to water.

    The US government is especially worried about the problem. That's why the Food and Drug Administration (FDA) is studying the health effects of caffeine on young people. Studies show that too much caffeine can make people nervous and unable to sleep. What's more, caffeine is habit-forming. Those who consume it regularly and stop suddenly may experience headaches and feel tired.

    One of the biggest concerns is the large amount of caffeine added to so-called energy drinks, like Red Bull. A 12-ounce can of cola has about 35 milligrams of caffeine. A similar serving of Red Bull contains more than three times that amount.

    The Institute of Medicine is also working on caffeine-safety measures. “Teenagers should not drink beverages that contain caffeine. They should be aware of caffeine's effects on health and on how the brain works. Take, for example, teenagers who consume caffeine to stay awake and study for a test. They will remember less of what they just studied,” said Stallings, a member of the institute.

    Companies that make products with added caffeine claim they do not advertise them to kids. However, there is no law to stop children from buying them. So the FDA needs to set limits on caffeine, especially in energy drinks. As for added caffeine in foods, the government should just say no. If not, the amount of caffeine should be printed on food labels to remind consumers. The government must do that.

    Doctors say kids should avoid caffeine. If you need extra energy, try these natural boosters: eat right, exercise, and get plenty of sleep.

    Introductory Chemistry was taught at Duke University for many years by professor Bonk. One year, two guys took the class and did pretty well on all the quizzes and mid terms. They each had a solid A. These two friends were so confident in going into the final that the weekend before finals week,despite the Chemistry final being on Monday,they decided to go to the University of Virginia to party with some friends.

    They had a great time there. However,with their hangovers(宿醉) and tiredness,they overslept all day Sunday and didn't make it back to Duke until early Monday morning. Rather than taking the final then,they found professor Bonk after the final and explained to him how they missed the final. They told him they went up to the University of Virginia for the weekend and had planned to come back in time to study,but they had a flat tire on the way back and didn't have a spare. So they were late getting back to campus.

    Bonk thought this over and agreed that they could take the final the following day. The two guys,happily and relieved,studied that night and went in the next day at the time that Bonk had told them. He placed them in separate rooms and handed each of them a test booklet. He told them to begin.

    They looked at the first problem which was something simple about solution(溶解).It was worth 5 points. "Cool," they thought,"this is going to be an easy final". They then turned the page. They were unprepared,however,for what they saw on it. The question contained only two words: (95 points) Which tire?

    What are the biggest problems that society will have to deal with in the new age? There re diseases like AIDS and cancer. There's climate change, of course. And what about producing enough cheap food and energy for the world's growing population? Who's going to solve all these terrible problems? Yes, politicians and world leaders will have a big part to play. Yes businesses will need to create the economic wealth to pay for some of these things. But who's going to make a much greater difference to something like AIDS or climate change. It's going to be a scientist. It is the scientist who can turn some new bit of science into a new technology to solve these problems. If you like thinking about the world around you, why not become a scientist? It doesn't mean you have to wear a white coat and plastic glasses and spend all your time in a lab as most people often imagine! Scientists do all kinds of amazing things that are actually interesting!

    Military scientists develop not only new weapons but new military technologies that could help make wars out of date. Forensic(法医的) scientists work with the police to find quite small clues to catch criminals. Scientists work in schools and colleges as the teachers and professors who will train tomorrow's scientists. Don't think a scientist is far away! Maybe you like cooking? You could be a food technologist helping to keep fruit and vegetables fresher for longer. Perhaps sport is your thing? Do you know that most top athletes work with sports scientists in order or improve their performance? You could even be the science writer who gets to spend the life studying the latest advances and sharing them with the world.

    Looking for something to do for the rest of your life? My advice? Take a long and hard look at science. It is interesting and ever.

All Aboard for a Family Trip by Train

    If you're looking for a family vacation idea, look no further. Explore America with Amtrak. On the train, your family will have plenty of room to spread out and relax.

    Once on board, the family can take in the scenery from the Sightseer Lounge（观景车厢）. Plus, most of our overnight trains feature Dining cars that serve three meals a day, with full menus and table service. If you're looking for lighter fare, grab a bite to eat or a drink in the Café car. You can also reserve Sleeping car accommodations and let the gentle rhythms of the train sway you to sleep. It's the best way to arrive at your destination rested and ready to go.

    Learn More about the Onboard Experience on www.amtrak.com

    A Dining Experience like No Other

    From full sit-down meals to more informal food service, many trains have one or more option for onboard dining. If you're not hungry, you might start to hear your stomach rumbling（腹鸣） after looking at our menus. We provide you with more dining choices, onboard dining reservations and the different types of dining cars, like long distance dinning car, lounge car and café car.

    Sleeping Accommodations

    Sleeping accommodations are available on most long-distance routes. Amtrak trains traveling on long-distance routes typically use either two-level Superliner or one-level Viewliner train car equipment, each of which include bedrooms arranged in various configurations and private and public bathrooms and showers.

    Seating Accommodations

    On most Amtrak trains, you have three options for seating accommodations. The availability of these options varies depending on your route and the type of train equipment in use:

    Coach Class: Designed for You to Relax.

    Business Class: More Amenities. More Comfort.

    First Class: Exclusively on Acela Express.

    Most dog owners believe their dogs experience guilt, but animal behaviorists say the "guilty look" of a dog is simply a reaction to you and that dogs lack the ability to feel shame.

    Alexandra Horowitz, a psychology professor and principal investigator at the Horowitz Dog Cognition Lab at Columbia University once carried out a study on dog "guilt". She videotaped 14 dogs in a series of trials and observed how they reacted when their owners left the room after instructing them not to eat a treat. When the owner was gone, Horowitz gave some of the dogs the forbidden treat. Then she would tell the owners whether their dogs had eaten the treat or had behaved. However, Horowitz wasn't always honest with them.

    Horowitz found that the dogs' "guilty looks" had little to do with whether they'd eaten the treat or not. In fact, dogs that hadn't eaten it but were scolded by misinformed owners tended to exhibit the most elements of the "guilty look".

Horowitz says this shows that the dogs' body language is actually a response to their owner's behavior—not an experience of shame for a misdeed. Why then, do dogs look so ashamed when we scold them?

Maybe that look of guilt is the result of a learned association. When you scold your dog for chewing up a pair of slippers, he quickly learns that if he lowers his head and tucks his tail, the undesirable response—raised voice and angry expression—is more likely to disappear.