Part of the fun of watching sports events is following an exciting rivalry (竞争关系).

    But where do all these rivalries come from?

    Some rivalries start because athletes spend a lot of time close to opponents (对手).

    Other rivalries get personal. Things that one rival says that are thought to be not respectful to the other can cause a rivalry, even if the words are misunderstood. And sometimes, rivalries grow just because the athletes don't like each other's personalities.

    Some sports may also be more likely than others to cause rivalries. “Some sports only meet a few times, so there is less chance for rivalries to build,” For example, in sports where athletes perform on their own, such as diving, rivalries might also take longer to appear than in sports in which athletes compete at the same time. But in tennis, players often face each other, and rivalries are more likely to happen.

    So do the rivalries do good or harm to the athletes?

    Some believe that rivalries can be a good thing because they encourage athletes to try harder to win. But rivalries can also become too personal, taking athletes' attention away from their sports.

    Keegan agreed that rivalries often do athletes more harm than good. “They can be a huge distraction (分散注意力的事) and lead to focusing on the opponent more than the game,” he said.

    “Top athletes often have physical and mental training that they follow in order to worry less and prepare to compete”, Gould further explained. An important part of that preparation is preventing from distractions, including rivalries.

    “The better athletes don't care too much about a rivalry – they try to treat every competition the same,” Gould told LiveScience.

    Traveling without a map in different countries, I find out about different ways of directions every time I ask “How can I get to the post office?”

    Foreign tourists are often puzzled in Japan because most streets there don't have name signs. In Japan, people use landmarks (地标) in their directions instead of street names. For example, the Japanese will say to travelers, “Go straight down to the corner. Turn left at the big hotel and go past a fruit market. The post office is across from the bus stop.”

    People in Los Angeles, the US, have no idea of distance on the map: they measure distance by time, not miles. “How far away is the post office?” you ask. “Oh,” they answer, “it's about five minutes from here.” You don't understand completely, “Yes, but how many miles away is it, please?” To this question you won't get an answer, because most probably they don't know it themselves.

    People in Greece sometimes do not even try to give directions because tourists seldom understand the Greek language. Instead, a Greek will often say, “Follow me.” Then he'll lead you through the streets of the city to the post office.

    Sometimes a person doesn't know the answer to your question. What happens in the situation? A New Yorker might say, “Sorry, I have no idea.” But in Yucatan, Mexico, no one answers “I don't know.” People there believe that “I don't” is impolite. They usually give an answer, but often a wrong one. So a tourist can get lost very easily in Yucatan! However, one thing will help you everywhere in the world. It's body language.

    While faking and fierce looks are among animals great defenses, many species know that everyone runs from a big stink (臭气) too.

    Vulture (秃鸳)

    Vultures, are street sweepers that feast on the rotting flesh of dead animals, which benefits us by ridding our highways and landscapes of animal bodies and the bacteria they might carry. When vultures feel threatened they vomit, and the smell of vomited-on dead bodies puts of most predators. Throwing up allows the vulture to fly away more quickly-and the vomit can hurt the aggressor's eyes and face.

    Opossum (负鼠)

    In some ways opossums have it easy. In order to become "dead", they don't have to fax anyone a death certificate. They just lie there with their tongues hanging out with the smell of dead flesh, sometimes for hours, effectively convincing potential predators they can find a much fresher meal elsewhere. Even if they keep getting attacked, they won't move any more than a human statue until the threat has passed.

    Hoatzin (磨雉)

    Hold your nose and meet the hoatzin, a bird of distinctions, not the least of which is that it smells like fresh cow shit. The animal mostly eats leaves and it's the only bird known to digest by fermentation, like a cow. This process is what causes its smell and has earned it the nickname the "stink bird

    Millipedes (千足虫)

    Millipedes are tricky. For starters they look wormy. Their name is deceptive, too: Their legs number about 750. Their major defense is to curl up into a ball. They, though, also release a harm eyes, and leave a horrible smell on their attackers.

    Sea Hare (海兔)

    The graceful sea hare is plain in taste in the first place, so it's not the most popular dish in the seafood chain. Nonetheless this type of sea creature has a pretty creative smell-related defense that is almost the opposite of its smelly companions on this list. The sea hare gives out a slimy, purple ink, the substance which makes food less palatable to predators.

    Researchers using lobsters (2-f) as model predators found that the sea blocks the lobsters receptive mechanism. In other words, the sea hare gives its attacker the equivalent of a stuffy nose so they don't know how appealing it is.

    There was a gardener who looked after his garden with great care. To water his flowers, he used two buckets(水桶).One was a shiny and new bucket. The other was a very old and dilapidated one, which had seen many years of service, but was now past its best.

    Every morning, the gardener would fill up the two buckets. Then he would carry them along the path, one on each side, to the flowerbeds. The new bucket was very proud of itself. It could carry a full bucket of water without a single drop spilled. The old bucket felt very ashamed(惭愧的)because of its holes: before it reached the flowerbeds, much water had leaked(渗漏)along the path.

    Sometimes the new bucket would say, "See how capable I am! How good it is that the gardener has me water the flowers every day! I don't know why he still uses you. What a waste of space you are!"

    And all that the old bucket could say was, "I know I am not very useful, but I can only do my best. I am happy that the gardener still finds a little bit of use in me, at least."

    One day, the gardener heard that kind of conversation. After watering the flowers as usual, he said, "You both have done your work very well. Now I am going to carry you back, and I want you to look carefully along the path."

    Then the two buckets did so. All along the path, they noticed, on the side where the new bucket was carried, there was just bare earth; on the other side where the old bucket was carried, there was a joyous row of wild flowers, leading all the way to the garden.

    The world's first hydrogen-powered trains have begun running in Germany. They began carrying passengers Monday in Germany's northern Lower Saxony state. The new train will run 100-kilometer trips and can travel up to 140 kilometers an hour.

    A French railroad company called Alstom built the two trains. Team in Germany and France cooperated on the project, which was supported by the German government. The new train model ,called the Coradia ilint, signals the beginning of efforts in Germany and other nations to move away from pollution-producing diesel(柴油) trains.

    The Coradia iLint is designed to run on non-electrified train lines with low levels of noise.

    It uses a process that combines hydrogen and oxygen to produce electrical power. If the system produces more energy than the train needs at that time, it can store the extra energy in batteries. The only emissions (排放物) are water and steam.

    A single tank of hydrogen can run a Coradia iLint train for about 1,000 kilometers. This is very similar to the distance a diesel-powered train can run on with a single tank.

    Hydrogen-powered trains cost more than diesel trains to build. But Alstom officials say the operating costs are much lower. The company plans to provide another 14 Coradia iLint trains to Lower Saxony by 2021.

    The head of railroad operations in the area, Carmen Schwab, praised replacing diesel trains with hydrogen. She said the move was an important first step in using clean-burning technologies to reach climate protection goals.

    Officials say the area's many wind turbines (涡轮机)will produce part of the energy to create the hydrogen to power the trains.

    Alstom says several other European countries have also expressed interest in developing hydrogen train systems. France has already said it wants its first hydrogen train to be operating by 2022.

    Most heroes are not super. They don't appear in comic books, on television, or in movies. They just do what they believe needs to be done to make their world a better place. Bike Batman is one of them.

    Bike Batman is a 30-year-old married engineer who lives in Seattle, Washington. He's a cyclist who also buys and sells bikes as a hobby.

    About three years ago, he was looking for a bike for his wife. He found one on Craigslist, a website where people list things they want to sell. As he often does, he also looked at Bike Index, a popular website that allows users to register their bikes and post reports when they're taken. The bike, which he was considering purchasing, clearly matched one reported stolen on Bike Index. Then he called the person who claimed to be the bike's owner and arranged to meet him-- supposedly to complete the sale. When the two men met, Bike Batman told the thief, "You've got two options. You can wait until a police officer gets here, or you can just get out of here." You can imagine what the thief did.

    After that first success, Bike Batman developed a safer routine. When he sees questionable bike ads on Craigslist, he cross-references the image with bikes reported on Bike Index. Once he has confirmed it with the owner, he arranges a meet-up with the thief and will call the Seattle police department so that officers can participate in the action. In more than half of the 22 cases in which he has got back and returned bikes, the thieves have been arrested. In one case, Bike Batman even helped a family recover a wide range of prized possessions that suspects had stolen during a home burglary.

    His nickname came from a discussion with a police officer who suggested he be called "Robin Hood". Since he wasn't exactly stealing from the rich and giving to the poor, "Batman" seemed a better fit. The idea of a superhero punishing criminals feels pretty silly to him, but the main reason he continues his work is to keep up Seattle's reputation as a friendly city.