Living in the wild can be hard. Finding food and staying safe aren't easy. Each day, animals struggle to survive in their habitats. Not all animals get by on their own. Some animals form a close partnership with other kinds of animals. These pairings are called symbiotic (共生的) relationships.

    In a symbiotic relationship, the animals depend on each other. One animal helps the other meet its needs. Sounds good, right? Not always. Some animals are not very kind to their partners. In some cases, one animal meets its needs but hurts its partner. Take ticks, for example. These insects suck blood to live. To get blood, they attach themselves to other kinds of animals. Ticks can pass germs that cause disease instead of helping their hosts.

    In other relationships, animals don't treat their partners so poorly Both animals benefit from living with the other animal.

    Small animals called cleaner shrimps have found a way of helping fish at coral reefs. As their name suggests, the shrimps clean the fish. They hang out at what scientists call a cleaning station. A fish stops by. Then a shrimp climbs onto the fish and even steps into the fish's mouth. The shrimp uses its tiny claws to pick stuff off the fish's body. That can include dead skin, tiny pieces of food, and wee creatures that can hurt the fish. The fish gets a nice cleaning. The shrimp enjoys a tasty meal offish trash.

    Small birds called plovers are also in the cleaning business. They have big customers—crocodiles. Crocs have long snouts（鼻子）filled with sharp teeth, Cleaning them is tricky. When a croc opens its mouth, the plover hops right in. The croc does not snap its snout shut. Instead, it lets the plover eat small, harmful animals attached to its teeth. The plover gets an easy meal while the croc gets clean teeth.

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    The human brain remembers negative experiences more easily than positive ones. Our brains have developed in this way because threats,like dangerous animals ,have a more immediate effect on people's survival compared to positive things like food or shelter.As a result,you clearly know what makes you unhappy,but do you know what makes you happy?

    Research suggests that our level of happiness is partly shaped by the choices we make.If you've been chasing wealth,fame,power and some material things,you may be looking for happiness in the wrong places.Psychologists suggest that the following habits can make people happier.

    People who own close relationships tend to be happier than those who do not.The number of our friends is not important.What matters is the quality of our relationships.Relationships that bring happiness usually consist of the sharing of feelings,acceptance,mutual respect and trust.

    People who exercise on a regular basis can improve both their physical and mental well-being.Some research has shown that exercise can be as effective as some medicine in treating depression.

    If we are so interested in an activity,we may lose track of time,and we can be in a state of flow.The activity could be playing the piano,surfing the Internet or playing a game...People who experience flow in their work or life tend to be happier.

    People are more likely to be happy if they know what their strengths are and can use them regularly.People are especially happy when they can set goals and use their strengths to achieve them.

    People,who think positively by being grateful,mindful and optimistic,are more likely to be happy.Being grateful means being thankful.Being mindful means considering,focusing on,and enjoying the experiences of the present moment.Being optimistic means being hopeful about the future.

    Age has never been a problem for 16-year-old Thessalonika Arzu-Embry. After all, she's already got her master's degree.

    The North Chicago-area teen started homeschooling at the age of 4. She began having an influence on others soon after. When she was 6 years old, she was an inspirational speaker at an organization called Tabitha House Community Service, a shelter for people who were forced to leave their homes due to the situations such as earthquake, flood and other natural disasters.

    At the age of 11, she graduated from high school and then earned her bachelor's degree in psychology in 2013. She completed those classes online as she was traveling for church events and leadership meetings.

    She doesn't stop there, though. The teen plans to focus on aviation psychology（航空心理学） for her further study, a decision inspired by her father who is a pilot. She grew up around airplanes and took fights all the time. Her goal is to use it to determine whether pilots are dealing with problems that could have deadly results once the plane takes off -- a topic that has been in the news lately. For her, it's a mix of two of her interests.

    In her free time, Thessalonika enjoys playing tennis, swimming and being active in her youth group at church. She also has three self-published books, which are on her site. Jump the Education Barrier is written to help students finish college, and in the future aims to help business owners with trends. Her third book The Genius Race, has a wider appeal. It is designed to help people to be geniuses in various areas of life.

    In 2001, British Prime Minister, Tony Blair said," We celebrate the diversity(多样性) in our country, get strength from the cultures and the races that go to make up Britain today."

    People from all cultures and races can be found in every corner of Britain and each person in his or her own way has contributed to making Britain the place it is today.

    If you walk down a street in Britain, especially in the bigger cities, you will usually see people with different hair, skin and eye colors. They may have white, brown or black skin and blonde, brown, black or red hair, with blue, black, brown or green eyes. Many of the people you will see will be British people but they all look different because the people of Britain are a mixed race.

    Britain is and has always been a mixed race society. Early in the British history they were invaded by Romans, Saxons, Vikings and Normans armies and later Africans were brought to Britain by force in the seventeenth and eighteenth centuries as slaves or servants. Over the years, thousands of people have been forced by persecution(迫害) or hunger to leave France, Ireland, Russia, and other countries, and have settled in Britain.

    About 8% of the population of Britain today are people from other cultures and races. That is 4.6 million people. According to a BBC report in September 2005, immigration (移民) made up more than half of Britain's population growth from 1991 to 2001.The Guardian newspaper reported in 2007 that the number of immigrants to the UK was 145,000 a year.

    People moving to Britain have brought their own cultures with them and try to keep them alive. An excellent example of this is the Notting Hill Carnival which celebrates the Caribbean culture and is now a very big part of British life today.

    Runners never forget crossing the finishing line at their first marathon, and that will be especially true for Mike Kohler. When Kohler crossed the starting line in Fargo last Saturday, he thought he was going to run 13.1 miles, his first half marathon. Six hours later, he had "mistakenly” completed his first full marathon, 26.2 miles.

    Kohler, a 26-year-old plumber (水管工) who now lives in West Fargo, had lined up for the half marathon that he hoped to complete in 150 minutes. He didn't realize he was in a starting fence with the full marathoners. Several miles later, Kohler began to realize he was on the course for the full marathon. "The 8-mile mark was when I figured out that I had made a mistake," he said. "Between then and 13.1, I debated with myself about what I should do."

    At some point — he doesn't remember when — he doubled down on the distance. "After I decided I was going to keep going, the thought of quitting didn't come back. Run, walk, or crawl, I wanted to finish," he said.

    Until Saturday, Kohler's longest race was a 10-kilometer run, just over 6 miles. Even the most casual marathoners do a training run of 18 miles before the race. From his experience, he said he learned one thing: sometimes people can do more than they think they can.

    After his long race, he went right back to work, put in a 10-hour day and then boarded a flight to Scotland for a vacation. "I was pretty sore, but I found the more I kept moving, the less sore I was, so I tried my best to go about life normally — minus running,” Kohler said from Glasgow. "I needed a break from that for a bit."

    Not for too long, though. He's already considering the Bemidji Blue Ox Marathon in October.