The discussion on renewable energy has been going on for at least a decade and people have relied on fossil fuels almost entirely for more than a century. However, the situation when fossil fuels were the most efficient and the cheapest source of energy has been left far in the past. Many countries such as Germany and Sweden have already made significant efforts to fix this situation, employing numerous power plants working on the renewable resources of energy. The most effective among these resources is geothermal（地热的）energy.

    Geothermal energy does not depend on the world's economic and political situation as strongly as fossil fuels do. Besides, extracting（提炼）fossil fuels adds to the price of energy produced from them. Therefore, geothermal energy is much cheaper than traditional ones, saving up to 80% of the costs over fossil fuels.

    Being a renewable resource, geothermal energy produces less waste and pollution than traditional energy sources. In geothermal systems, carbon dioxide makes up about 10% of air produced. Overall, in order to produce the electricity that can be used for one hour, the geothermal systems produce 0.1 pound of carbon dioxide and other harmful gases. For a comparison, a power plant producing from gas produces up to 2 pounds of carbon dioxide into the atmosphere, and those power plants that work on coal（煤）produce an astonishing 3.6 pounds of greenhouse gases.

    Low costs is another reason why using geothermal power plants should be the first choice for many countries. Geothermal heat systems require 25% to 50% less energy for work compared with the traditional systems for heating or cooling. Besides, geothermal equipment is less big: due to the very nature of geothermal energy, geothermal power plants have only a few moving parts, all of which can be easily sheltered inside a relatively small building. What's more, the life span of geothermal equipment is rather long. All these make geothermal power stations easy to build and keep.

    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 views, 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 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

    Noteworthy 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 an off-leash area on the park's west end that lets dogs run free.

    Buena Vista Dog Park

    At 146 years young, 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.

    Here are some of the strangest aviation(航空)ideas in recent history.

    Double-Decker Seating

    In 2015, Airbus filed a patent for a design for a double-decker cabin seating arrangement. Passengers would sit on top of the other, with upper-tier passengers climbing steps or a small ladder to reach their seats. While the design does have some advantages, the idea of climbing a ladder during flight seems unreliable.

    Separated Cabins

    This patent was awarded to Airbus. Rather than waiting for a flight to arrive and be cleaned,passengers could simply board a ready cabin, which would be moved into the plane's body as soon as it was ready. When the plane reached its destination, the cabin would be separated again. Different cabins with different kinds of seating or levels of comfort could be used for flights of different lengths or destinations.

    Windowless Cockpits(驾驶舱)

    For ideal design, airplane noses should be long and pointy. But there's the whole "pilots have to fit in the cockpit" problem. Well, what if the cockpit didn't have to go in the nose of the plane? That's part of the thinking behind this Airbus patent application* which suggests replacing the plane's window with a digital viewing surface. Without a window, there's no reason the cockpit needs to go in the front of the plane —it could go in the middle of the plane, or even in the tail.

    Nap Straps (睡眠吊带)

    Airbus is not the only company in the strange patent contest. Boeing's got its own patent, Nap Straps. With this invention, passengers looking for a nap can find an "upright sleep system^" beneath their seat. In action, the whole thing is somewhat like a traction device for someone who's been in a terrible accident.

Visit Chicago Children's Museum

    In brief:

    This museum offers plenty of fun hands-on activities for kids. However, this is one of the few Chicago museums not "fun for the whole family" as adults and older kids will be bored to tears.

    Address: 700 East Grand Ave. (Navy Pier), Chicago

    Phone: 312- 527-1000

    Public transportation:

    CTA bus lines # 29 (State Street), #65 (Grand Avenue), and # 66 (Chicago Avenue) all serve Navy Pier.

    Parking fees:

    · Monday through Thursday: $ 20

    · Friday through Sunday: $ 24

    · Holidays: $ 24

    Opening hours:

    · Weekdays: 10 a. m.-5 p. m

    · Weekends: 10 a. m.-8 p. m

    Entrance fees:

    ·Adults: $12

    ·Children: $12

    ·Seniors (65+): $11

    ·Children (under 5): free

    Activities:

    Located at one of Chicago's top tourist attractions, Navy Pier, the museum offers three floors of activities for kids, including:

    ·Play It Safe—all about home safety

    ·Inventing Lab—provides parts and instructions for creating things

    ·Kids Town—a playroom recreating a Chicago neighborhood where kids can pretend to do things like shopping for groceries and driving a CTA bus

    ·Climbing Schooner—a three-floor climbing building

    ·My Museum—kids get to create various pieces of art that are "all about me"

    ·Skyline—kids learn about skyscrapers and design their own buildings

    ·Tree House Trails—a play area designed like a forest

    ·Waterways—water activities showing how pumps and dams work

When I grow up

    In kindergarten, my class was asked to draw pictures, showing what we wanted to be when we grew up. Our drawings were expected to display our dream occupations. I remember pictures of ballerinas dancing, firefighters putting out a blaze, and astronauts leaping across the moon.

    My picture showed a figure with brown hair holding a box of orange juice beside a counter. Underneath was my handwriting: "When I grow up, I want to work at Market Basket because it would be fun to swipe (刷) orange juice across the scanner." Out of everything, my five­year­old self wished to work at the local grocery store.

    When we are young, questions of what we want to be when we grow up are common. Yet we are not expected to respond with an answer that is likely to come true. However, when we become teens, we are asked the very same questions twice as often. The difference is, now we are supposed to answer with confidence.

    Teens are expected to know exactly what we want to be and how we are going to achieve that goal. However, not all of us can be so sure. Even though I am in high school, I cannot answer with certainty. But I don't consider that a bad thing. How am I supposed to know what I will want to spend my time doing at age 40?

    When I think about the future, I definitely don't see myself working at Market Basket, but in reality, if that was what would make me happy, I would do it. So, the next time someone asks me what I want to be when I grow up, I will simply say "happy".

    Happiness is a destination for everyone. We may want to walk different paths in life, but we all want to be happy wherever we end up. Choose your path, but don't worry too much about choosing wisely. Make a mistake or two and try new things. But always remember, if you're not happy, you're not at the end of your journey yet.

Human speech contains more than 2,000 different sounds, from the common "m" and "a" to the rare clicks of some southern African languages. But why are certain sounds more common than others? A groundbreaking, five-year study shows that diet-related changes in human bite led to new speech sounds that are now found in half the world's languages. 

More than 30 years ago, the scholar Charles Hockett noted that speech sounds called labiodentals, such as "f" and "v", were more common in the languages of societies that ate softer foods. Now a team of researchers led by Damián Blasi at the University of Zurich, Switzerland, has found how and why this trend arose. 

They discovered that the upper and lower front teeth of ancient human adults were aligned(对齐), making it hard to produce labiodentals, which are formed by touching the lower lip to the upper teeth. Later, our jaws changed to an overbite structure(结构), making it easier to produce such sounds. 

The team showed that this change in bite was connected with the development of agriculture in the Neolithic period. Food became easier to chew at this point. The jawbone didn't have to do as much work and so didn't grow to be so large. 

Analyses of a language database also confirmed that there was a global change in the sound of world languages after the Neolithic age, with the use of "f" and "v" increasing remarkably during the last few thousand years. These sounds are still not found in the languages of many hunter-gatherer people today. 

This research overturns the popular view that all human speech sounds were present when human beings evolved around 300,000 years ago. "The set of speech sounds we use has not necessarily remained stable since the appearance of human beings, but rather the huge variety of speech sounds that we find today is the product of a complex interplay of things like biological change and cultural evolution," said Steven Moran, a member of the research team.