"Can't hold a candle to" is a popular expression. When there wasn't electricity, someone would have a servant light his way by holding a candle. The expression meant that the person who cannot hold a candle to you is not fit even to be your servant. Now，it means such a person cannot compare or compete.

    Another expression is "hold your tongue. "It means to be still and not talk. "Hold your tongue" is not something you would tell a friend. But a parent or teacher might use the expression to quiet a noisy child.

    "Hold out" is an expression one hears often in sports reports and labor news. It means to refuse to play or work. Professional football and baseball players "hold out" if their team refuses to pay them what they think they are worth.

    The expression "hold up" has several different meanings. One is a robbery. A man with a gun may say, "This is a hold up. Give me your money." Another meaning is to delay. A driver who was held up by heavy traffic might be late for work. Another meaning is for a story to be considered true after an investigation. A story can hold up if it is proved true.

    "Hold on" is another expression, which means wait or stop. As you leave for school, your brother may say, "Hold on，you forgot your book. " It is used to ask a telephone caller to wait and not hang up his telephone.

    Our final expression is "hold the line." That means to keep a problem or situation from getting worse—to hold steady. For example, the president may say he will "hold the line on taxes." He means therewill be no increase in taxes.

    It's never easy to explain exactly when a specific language began, and in the case of English we can hardly regard it as a separate language before the Anglo-Saxons came to Britain. Germanic invaders (入侵者) came and settled in Britain from the north-western coastline of continental Europe in the fifth centuries. The invaders all spoke a language that was Germanic (related to Dutch, Frisian, German and the Scandinavian languages), but we'll probably never know how different their speech was from that of their continental neighbors.

    The reason that we know so little about the language in this period is because we do not have much in the way of written records from any of the Germanic languages until several centuries later. When Old English writings began to appear in the seventh and eighth centuries there was a good deal of regional variation (变化), but not more than that found in later periods.

    The Celts already lived in Britain when the Anglo-Saxons arrived, but there are few obvious signs of their language in English today. Some scholars have suggested that the Celtic tongue might have had some influence on the grammatical development of English, particularly in some parts of the country, but this is highly speculative (猜测). The number of borrowed words that have entered Old English from this language is very small. Those that survive in modern English include “comb” (a type of valley), alongside some place names.

    Think plants are just boring green things that you use for food and decoration? Think again! Plants are able to do some pretty awesome things that you're probably totally unaware of.

    Researchers have discovered that plants have the ability to communicate with an underground network made up of fungus (真菌) , which serves the plants in many ways. Tomato plants use the fungus web to warn each other of their own unhealthy conditions. Trees connected through the fungus network could move nutrients (养分) to and from each other. It is believed that larger trees move nutrients to smaller ones to help them to survive.

    Not only that, but they can also damage unwelcome plants by spreading poisonous chemicals through the fungus. It sounds like the plant world had the Internet before we did.

    Some plants have a rather impressive line of defense against being eaten. When sensing they are being swallowed, they give off a chemical into the air that attracts the insect's natural enemy. The enemy attacks the bug, thus saving the plants. This is basically the plant kingdom version of getting your older brother to beat up that kid who steals your lunch money.

    You might be aware that humans and animals have an internal clock. But did you know that plants also have this clock? This means they can prepare for certain times of day just like we do. Is it because they can react to light at sunrise? In a study, scientists found that plants use the sugars they produce to keep time, which help to regulate the genes responsible for the plant's own internal clock. So, in a sense, wake up with petunias (矮牵牛) is just as valid as ―wake up with the chickens.

    Nature is full of surprises. So for those of you who didn't know the wonders of plants, now you do.

    A year back I received a full scholarship to attend the University of San Francisco. All of my hard work had paid off. My mom had spent a lot in my attending a private high school, so I made sure to push myself: I volunteered, got involved in various clubs, and graduated with honors. I was so excited to start a new chapter(篇章)of my life. I had totally packed two weeks before it was time to leave.

    Soon enough, the big day came, but it wasn't like what I had thought. The first two weeks were the most difficult days of my entire life. Every night I would cry myself to sleep. I was so homesick and I didn't know how to deal with my broken heart. To distract myself, I threw myself into my studies and I applied for a ton of jobs. In any remaining free time, I started forcing myself to the gym. I wanted to keep every part of my day busy so I wouldn't think how lonely I felt.

    Soon after, I began to limit food, and then I became worse. Finally, I went to see a doctor. When the doctor weighed me, I was crazy about the number of my weight. So I continued to lower my goal, and convinced that controlling this number was the solution for my homesickness. But when I was told that I had no choice but to spend time on my studies. I quickly started recovery in my mind.

    How could I do? I told myself that school was what I was best at. I decided to get rid of my homesickness and took exercise actively. My first term of college had passed by at last and I had gotten straight A's. That's why I want to share my story－to help other students feel less lonely.

    Like infectious diseases, ideas in the academic world are epidemic (传染的). But why some travel far and wide while equally good ones has been a mystery? Now a team of computer scientists has used an epidemiological model to simulate (模仿) how ideas move from one academic institution to another. The model showed that ideas originating at famous institutions caused bigger "epidemics" than equally good ideas from less famous places, explains Allison Morgan, a computer scientist at the University of Colorado Boulder.

    "This implies that where an idea is born shapes how far it spreads," says senior author Aaron Clauset.

    Not only is this unfair— "it reveals a big weakness in how we're doing science," says Simon DeDeo, a professor of social and decision sciences at Carnegie Mellon university, who was not involved in the study. "There are many highly trained people with good ideas who do not end up at top institutions. They are producing good ideas, and we know those ideas are getting lost," DeDeo says. "Our science, our scholarships, is not as good because of this."

    The Colorado researchers first looked at how five big ideas in computer science spread to new institutions. They found that hiring a new faculty member accounted for this movement a little more than a third of the time--and in 81 percent of those cases, transmissions took place from higher – to lower-prestige (声望) universities. Then the team simulated the spread of ideas using an infectious disease model and found that the size of an idea "epidemic" depended on the prestige of the originating institution.

    The researchers' model suggests that there "may be a number of quite good ideas that originate in the middle of the pack, in terms of universities." Clauset says. There is a lot of good work coming out of less famous places, he says: "You can learn a huge amount from it, and you can learn things that other people don't know because they're not even paying attention."