Since English biologist Charles Darwin published On the Origin of Species in 1859, scientists have vastly improved their knowledge of natural history. However, a lot of information is still of the speculation, and scientists can still only make educated guesses at certain things.

    One subject that they guess about is why some 400 million years ago, animals in the sea developed limbs (肢) that allowed them to move onto and live on land.

    Recently, an idea that occurred to the US paleontologist (古生物学家) Alfred Romer a century ago became a hot topic once again.

    Homer thought that tidal (潮汐的) pools might have led to fish gaining limbs. Sea animals would have been forced into these pools by strong tides. Then, they would have been made either to adapt to their new environment close to land or die. The fittest among them grew to accomplish the transition (过渡) from sea to land.

    Romer called these earliest four-footed animals “tetrapods”. Science has always thought that this was a credible theory, but only recently has there been strong enough evidence to support it.

    Hannah Byrne is an oceanographer (海洋学家) at Uppsala University in Sweden. She announced at the 2018 Ocean Sciences Meeting in Oregon, US, that by using computer software, her team had managed to link Homer's theory to places where fossil deposits (沉积物) of the earliest tetrapods were found.

    According to the magazine Science, in 2014, Steven Balbus, a scientist at the University of Oxford in the UK, calculated that 400 million years ago, when the move from land to sea was achieved, tides were stronger than they are today. This is because the planet was 10 percent closer to the moon than it is now.

    The creatures stranded in the pools would have been under the pressure of “survival of the fittest”, explained Mattias Green, an ocean scientist at the UK's University of Bangor. As he told Science, “After a few days in these pools, you become food or you run out of food... the fish that had large limbs had an advantage because they could flip (翻转) themselves back in the water.”

    As is often the case, however, there are others who find the theory less convincing. Cambridge University's paleontologist Jennifer Clark, speaking to Nature magazine, seemed unconvinced. “It's only one of many ideas for the origin of land-based tetrapods, any or all of which may have been a part of the answer,” she said.

    “Belittle” was first used by Thomas Jefferson, the third president of the United States.

    Many years ago, Buffon, a French naturalist, wrote some books about natural history. The books were a great success even though some critics did not like them. Some critics said, “Buffon is more of a poet than a scientist.”

    Thomas Jefferson did not like what Buffon had said about the natural wonders of the New World. It seemed to Jefferson that Buffon had spoken of natural wonders in America as if they were unimportant.

    This troubled Thomas Jefferson. He was a naturalist, as well as a farmer, inventor, historian, writer and politician. He had seen the natural wonders of Europe. To him, they were no more important than those of the New World.

    In 1788, Thomas Jefferson wrote about his home state, Virginia. While writing, he thought of its natural beauty and then of the words of Buffon. At that moment, Jefferson created a new word－belittle. He said, “Buffon believes that nature belittles her productions on this side of the Atlantic.”

    Noah Webster, the American word expert, liked this word. He put it in his English language dictionary in 1806, “Belittle－to make somebody or something small, unimportant.”

    Americans had already accepted Jefferson's word and started to use it. In 1797, the Independent Chronicle newspaper used the word to describe a politician the paper supported. “He is an honorable man,” the paper wrote, “so let the opposition try to belittle him as much as they please.

    In 1872, a famous American word expert decided that the time had come to kill this word. He said, “'Belittle' has no chance of becoming English. And as more critical writers of America, like those of Britain, feel no need of it, the sooner it is forgotten, the better.” This expert failed to kill the word. Today, “belittle” is used where the English language is spoken.

    Have you ever run into a careless cell phone user on the street? Perhaps they were busy talking, texting or checking updates on We Chat without looking at what was going on around them. As the number of this new “species” of human has kept rising, they have been given a new name—phubbers (低头族).

    Recently, a cartoon created by students from China Central Academy of Fine Arts put this group of people under the spotlight. In the short film, phubbers with various social identities bury themselves in their phones, a doctor plays with his cell phone while letting his patient die, a pretty woman takes selfe in front of a car accident site, and a father loses his child without knowing about it while using his mobile phone, a chain of similar events eventually leads to a series of destruction.

    Although the ending sounds overstated, the damage phubbing can bring is real.

    Your health is the first to bear the consequence (后果) of it. “Constantly bending your head to check your cell phone could damage your neck,” Guangming Daily quoted doctors as saying. “The neck is like a rope that breaks after long-term stretching.” Also, staring at cell phones for long periods of time will damage your eyesight gradually, according to the report.

    But that's not all. Being a phubber could also damage your social skills and drive you away from your friends and family. At reunions with family or friends, many people tend to stick to their cell phones while others are chatting happily with each other and this creates a strange atmosphere, Qilu Evening News reported.

    It can also cost you your life. There have been lots of reports on phubbers who fell to their death, suffered accidents, and were robbed of their cell phones in broad daylight.

    Despite what so many people would love to believe, NASA hasn't discovered any evidence of past or present intelligent life on Mars. Therefore, when the Curiosity rover (好奇号探测器) found something suspicious on the Red Planet's surface, they were not only surprised but also a little bit worried.

    The thin fragment(碎片) was suspicious enough to guarantee its own name, with NASA's Curiosity rover team calling it the "Pettegrove Point Foreign Object Debris", named for where it was discovered. With no idea what it was or where it came from, the rover's handlers began to worry that it might actually be a piece of the rover itself, suggesting some unseen damage or other issue with the robot. Thankfully, those concerns seem to have been unfound.

    In a new update from NASA the object has now been identified as a natural piece of rock rather than a piece of any man-made craft or vehicle. The team analyzed the unusual object with a tool called the Chem Cam RMI. The instrument uses a laser (激光器)to sniff out the makeup of anything that is pointed at, and the results for this particular piece of debris revealed that it's actually just a very thin piece of rock.

    NASA describes the inspection: The planning day began with an interesting result from the previous plan's Chem Cam RMI analysis of a target that was referred to as "Pettegrove Point Foreign Object Debris"(PPFOD)，and supposed to be a piece of spacecraft debris fact. In fact it was found to be a very thin slice of rock, so we can all rest easy tonight. Curiosity has not begun to shed its skin!

    How this particularly thin sliver of rock got to where it is—and why it seems to be a different colour than the surrounding sand and debris—remains unexplained, but at least the rover isn't falling apart.

It's necessary to revise(复习) after lessons so that you can really understand, remember and use what you have learned. It is also important to revise before exams. {#blank#}1{#/blank#}. 

    Find Your Place. To revise for an exam, you must first find a quiet and relaxing environment. {#blank#}2{#/blank#} It should also be a place where you will not be disturbed.

    Take Your Time. It's a good idea to make revising part of your weekly routine. The best way to do this is to revise every school day. {#blank#}3{#/blank#} Make sure that you study for no more than two hours every time, and that you take a little rest every half hour or so. This will keep you fresh and able to take in information.

    Stay Organized. {#blank#}4{#/blank#} If you are taking notes, organize them by subject, topic and date. That way when you have an exam, you can easily find the right notes to study to help you prepare.

 {#blank#}5{#/blank#} At the end of every revision, review your notes carefully to check that you have understood what you have learned. You may also consider writing out revision cards. You can then use these as summary of the subjects that you have learned.

A. Get Ready.

B. Check Your Progress.

C. It takes time to learn a new language.

D. But don't revise for too long at a time.

E. Here is some advice on how to revise well.

F. A place where you feel comfortable works best.

G. It is helpful to set up a system so you are organized.

After a busy morning, lunch can feel like just the pick-me-up you need-but sometimes the meal that you thought would energize you is the very thing that makes you want to nap at your desk.

Feeling tired after lunch, or post-meals in general, is known as postprandial somnolence—or, colloquially, the food coma.

Part of this phenomenon is due to basic physiology (生理学): When humans eat, most of our blood goes to the digestive organs to process the food, said Sandra Arévalo, director of community health and wellness at Montefiore Nyack Hospital in New York state.

The tendency to get tired after eating isn't inherently suggestive of something amiss (出错的). But there can be additional factors that worsen this natural response, making getting through the rest of the workday or any activities feel like a slog. Here's what to watch out for and how to make adjustments.

When it comes to why you feel overly tired after eating, a common cause is consuming meals that are heavy in terms of quantity or quality. Not eating breakfast can lead to overindulging later in the day if excessive (过度的) hunger makes controlling your appetite difficult, Arévalo said.

Sometimes, however, the makeup of certain foods can contribute to tiredness. Fats are the hardest nutrient to digest because their molecules are much larger than those of protein or carbs, said Julie Stefanski, a spokesperson for the Academy of Nutrition and Dietetics. If you had a meal high in fat—such as fried foods or pizza—that could make you feel tired. Meals high in added sugar or refined or highly processed carbohydrates can have the same effect.

The fiber in so-called whole foods like corns slows the absorption of sugar into the body, which means they don't cause blood sugar or insulin spikes and instead give you more stable, lasting energy, said Kristin Kirkpatrick, a registered dietitian at the Cleveland Clinic.

"A five-minute walk or something helps to improve circulation and alertness (机敏), as well," Arévalo said.