Grammar is the system of a language. People sometimes describe grammar as the “rules” of a language; but in fact no language has rules. If we use the word “rules”, we suggest that somebody created the rules first and then spoke the language, like a new game. But languages did not start like that. Languages started by people making sounds which evolved (逐渐发展成) into words, phrases and sentences. No commonly-spoken language is fixed. All languages change over time. What we call “grammar” is simply a reflection (反映) of a language at a particular time.

    Do we need to study grammar to learn a language? The short answer is “no”. Very many people in the world speak their own, native language without having studied its grammar. Children start to speak before they even know the word“grammar”. But if you are serious about learning a foreign language, the long answer is “yes, grammar can help you to learn a language more quickly and more efficiently.” It's important to think of grammar as something that can help you, like a friend. When you understand the grammar (or system) of a language, you can understand many things yourself, without having to ask a teacher or look in a book.

So think of grammar as something good, something positive, something that you can use to find your way—like a signpost(路标) or a map.

    Except invented languages like Esperanto（世界语）. And if Esperanto were widely spoken, its rules would soon be very different.

    More and more people like bicycling and it is no surprise. It is fun, healthy and good for the environment. Maybe that's why there are 1.4 billion bicycles and only 400 million cars on roads worldwide today. Bikes can take you almost anywhere, and there is no oil cost!

    Get on a bicycle and ride around your neighbourhood. You may discover something new all around you. Stopping and getting off a bike is easier than stopping and getting out of your car.

    You can bike to work and benefit (受益) from the enjoyable exercise without polluting  the environment. You don't even have to ride all the way. Folding (折叠) bikes work well for people who ride the train. Just fold the bike and take it with you. You can do the same on an airplane. A folding bike can be packed in a suitcase. You can also take a common bike with you when you fly. But be sure to look for information by getting on airline websites. Not all airlines are bicycle-friendly to travellers.

Health Benefits of Bicycling:

    It helps to prevent heart diseases.

    Bicycling helps to control your weight.

    A 15-minute bike ride to and from work three times a week burns off five kilos of fat in a year.

    Bicycling can improve your mood (心情).

    Exercise like bicycling has been shown to make people feel better, more relaxed and self-confident.

    Bicycling is healthier than driving.

    Dr. Sasaki knew the first-night effect probably has something to do with how humans evolved.

    The puzzle was what benefit would be gained from it when performance might be affected the following day. She also knew from previous work conducted on birds and dolphins that these animals put half of their brains to sleep at a time so that they can rest while remaining alert enough to avoid predators (捕食者). This led her to wonder if people might be doing the same thing. To take a closer look, her team studied 35 healthy people as they slept in the unfamiliar environment of the university's Department of Psychological Sciences. The participants each slept in the department for two nights and were carefully monitored with techniques that looked at the activity of their brains. Dr. Sasaki found, as expected, the participants slept less well on their first night than they did on their second, taking more than twice as long to fall asleep and sleeping less overall. During deep sleep, the participants' brains behaved in a similar manner seen in birds and dolphins. On the first night only, the left hemispheres (半球) of their brains did not sleep nearly as deeply as their right hemispheres did.

    Curious if the left hemispheres were indeed remaining awake to process information detected in the surrounding environment, Dr. Sasaki re-ran the experiment while presenting the sleeping participants with a mix of regularly timed beeps (蜂鸣声) of the same tone and irregular beeps of a different tone during the night. She worked out that, if the left hemisphere was staying alert to keep guard in a strange environment, then it would react to the irregular beeps by stirring people from sleep and would ignore the regularly timed ones. This is precisely what she found.

    The sharing economy, represented by companies like Airbnb or Uber, is the latest fashion craze. But many supporters have overlooked the reality that this new business model is largely based on escaping regulations and breaking the law.

    Airbnb is an Internet-based service that allows people to rent out spare rooms to strangers for short stays. Uber is an Internet taxi service that allows thousands of people to answer ride requests with their own cars. There are hundreds of other such services.

    The good thing about the sharing economy is that it promotes the use of underused resources. Millions of people have houses or apartments with empty rooms, and Airbnb allows them to profit from these rooms while allowing guests a place to stay at prices that are often far less than those charged by hotels. Uber offers prices that are competitive with standard taxi prices and their drivers are often much quicker and more trustworthy.

    But the downside of the sharing economy has gotten much less attention. Most cities and states both tax and regulate hotels, and the tourists who stay in hotels are usually an important source of tax income. But many of Airbnb's customers are not paying the taxes required under the law.

    Airbnb can also raise issues of safety for its customers and trouble for hosts' neighbors. Hotels are regularly inspected to ensure that they are not fire traps and that they don't form other risks for visitors. Airbnb hosts face no such inspections.

    Since Airbnb is allowing people to escape taxes and regulations, the company is simply promoting thefts. Others in the economy will lose by bearing an additional tax burden or being forced to live next to an apartment unit with a never-ending series of noisy visitors.

    The same story may apply with Uber. Uber is currently in disputes over whether its cars meet the safety and insurance requirements imposed on standard taxis. Also, if Uber and related services flood the market, they could harm all taxi drivers' ability to earn a minimum wage.

    This downside of the sharing needs to be taken seriously, but that doesn't mean the current tax and regulatory structure is perfect.

    If you're new to San Francisco, paying the city a visit, or simply looking for a new playground for you and your dog, here are four of the finest dog parks in San Francisco.

    Corona Heights Dog Park

    Often visited by residents from all over the city because of its nearness to the Randall Museum, Corona Heights Dog Park offers pets and owners breathtaking view after a steep hillside climb, and a fenced dog area that allows dogs to let loose without a leash（狗链）. Owners will also enjoy the playground, tennis courts and basketball courts.

    Dolores Dog Park

    The grounds of Dolores Park once served as camps for those who were left homeless by the 1906 earthquake, but now are often visited by crowds of Mission District people. Four-legged friends can also wander about carefree off-leash while making friends with other members of the doggie community.

    Pine Lake Dog Park

    Famous for its place as a rest stop for hundreds of species of birds to fly to and from warmer climates, Pine Lake Park is also prized by city dogs and their owners for their nice hiking paths, picturesque lake suited for swimming, and off-leash area on the park's west end that lets dogs run free.

    Buena Vista Dog Park

    With a history of 146 years, Buena Vista Park is San Francisco's oldest park. Dogs and owners with plus energy will love burning it on this park's steep paths and winding staircases. Dog owners should have good control over their dogs, as it's quite easy for dogs to get separated when going through Buena Vista's many twists and turns.

    A new collection of photos brings an unsuccessful Antarctic voyage back to life. Frank Hurley's pictures would be outstanding — undoubtedly first-rate photo-journalism — if they had been made last week. In fact, they were shot from 1914 through 1916, most of them after a disastrous ship wreck (海滩) by a cameraman who had no reasonable expectation of survival Many of the images were stored in an ice chest under freezing water, in the damaged wooden ship.

    The ship was the Endurance a small tight Norwegian-built three-master that was intended to take Sir Ermest Shackleton and a small crew of seamen and scientists, 27 men in all, to the southernmost shore of Antarctica's Weddell Sm. From that point Shackleton wanted to force a passage by dog sled across the continent. The journey was intended to achieve more than what Captain Robert Falcon Scott had done. Captain Scott had reached the South Pole early in 1912 but had died with his four companions on the march back.

    As writer Caroline Alexander makes clear in her forceful and well-researched story The Endurance、adventuring was then a thoroughly commercial effort Scott's last journey, completed as he lay in a tent dying of cold and hunger, caught the world's imagination, and a film made in his honor drew crowds Shackleton, a onetime British merchant-navy officer who had got to within 100 miles of the South Pole in 1908,started a business before his 1914 voyage to make money from movie and still photography. Frank Hurley，a confident and gifted Australian photographer who knew the Antarctic, was hired to make the images most of which have never before been published.