When the Normans built their first simple wooden castles in England，they built them on the top of small hills.The first permanent castles were made of stone and built with thick walls.The main building was usually surrounded by walls which overlooked the moat (护城河)．

     The entrance to the castle was usually over a drawbridge (吊桥) leading to the main gatehouse.The drawbridge could be raised or lowered and an iron grille (栅栏) could be lowered to shut off the entrance to the gatehouse.

     As time went on，the castle builders became more advanced in their techniques.Instead of building a strong central building and surrounding it with walls of lesser strength，they thought out the idea of surrounding a central area with huge walls which could contain all the main rooms of the castle.These walls usually had many towers and these towers were really a series of main buildings along the castle walls.In building these castles they used hill sites whenever possible in order to give the castle a better position.Because the outside world was shut off by a barrier or curtain of defences，they are called “curtain wall” castles.

     With the passing of time there was less need to build strong castles and nobles built manor (庄园) houses.These manor houses often had battlements and iron grilles，but they were built more for comfort and included many of the conveniences and luxuries of the large houses which were being built in the towns.

     Unfortunately，many English castles were damaged or destroyed completely during the Civil Wars of the 1600s.

    The vast majority of people can buy pretty much anything they need. Not anything they want, necessarily, but anything they need to achieve a satisfactory degree of creature comfort: clothing, water, shoes and food.

    During my childhood, a Michael Pollan book would have been the prize of my year, were I to find it waiting under my Christmas tree or open it upon my birthday. I also used to be thrilled at receiving necessary things, like simple socks or gloves, as present. Nowadays I have too many gloves. I purchase leather gloves online that appear to be a good deal or just because I like their look.

    Prosperity (富足) is a good thing, right? Yes, of course. But for me, I find that the greater ease with which such a generous gift is purchased, the less significance it has when given. This is why I try harder at gifts.

    My first line of dealing with this problem is simply understanding the effect of a little time spent. Even writing out a thoughtful or funny card goes a lot further than a “cute top” purchased from a popular shopping website.

    Need help? Go to your printer. There's paper in there. Fold one sheet in half and draw a heart on the front. Open it up and fill the card with a poem or a few words of your own. Not only is it obvious that you took the time to select your words and write them down, but now you force the reader to stop for a short time and consider what you were trying to accomplish with them. The effort made by the two of you is the gift.

    No matter how you decide to spend a little more time on your giving, the point is just quite simply that you do. You don't have to give a person a handmade paper boat to get a reaction. But you won't be sorry if you do.

    When it comes to the most famous 20^th century painters of the United States, Grandma Moses should be mentioned, although she did not start painting until she was in her late seventies. As she once said to herself:" I would never sit back in a rocking chair, waiting for someone to help me." No one could have had a more active old age.

    She was born on a farm in New York State, one of five boys and five girls. At 12 she left home and was in domestic service until at 27 she married Thomas Moses, the hired hand of one of her employers. They farmed most of their lives, first in Virginia and then in New York State, at Eagle Bridge. She had ten children, of whom five survived; her husband died in 1927.

    Grandma Moses painted a little as a child and made embroidery(刺绣) pictures as a hobby, but only changed to oils in old age because her hands became too stiff(僵硬的) to sew and she still wanted to keep busy and pass the time. Her pictures were first sold at the local drugstore and at a market and were soon noticed by a businessman who bought all that she painted. Three of the pictures were exhibited(展览) in the Museum of Modern Art, and in 1940 she had her first exhibition in New York. Between the 1930's and her death, she produced some 2,000 pictures: careful and lively portrayals of the country life she had known for so long, with a wonderful sense of color and form. "I think really hard till I think of something really pretty, and then I paint it" she said.

    The New York See It All Tour is exactly what it sounds like: an all-inclusive guided tour of New York City.

    Central Park

    One of the most famous parks in the world, Central Park is a man-made wonder. Not only is it the first public park built in America, but it is also one of the most frequently visited parks, with over 25 million guests per year. Set in the middle of busy Manhattan, its grounds serve as a safe harbor, not only for athletes, and musicians but also for lots of migratory birds each year. One can spend an entire peaceful day wandering its grounds, gazing upon nearly 50 fountains, monuments, and sculptures or admiring its 36 bridges.

    Hudson River Park

    Hudson River Park is a waterside park on the Hudson River that extends from 59th Street south to Battery Park in the New York City district of Manhattan. Bicycle and pedestrian paths, including the Manhattan Waterfront Greenway, span the park north to south, opening up the waterfront for the public to relax. The park includes tennis and soccer fields, children's playground, dog run, and many other features.

    Washington Square Park

    Washington Square Park, located in the heart of Greenwich Village, is a very popular and often crowded square. People from all backgrounds gather to this large square dotted with trees.

    Central Park Zoo

    The Central Park Zoo is a small 6.5-acre zoo located on Central Park in New York City. The zoo began in the 1860s, making it the first official zoo to open in New York. The zoo was improved in 1934, with the addition of many new buildings ranged in a quadrangle around the sea lion pool. Finally, the zoo was repaired in the mid-1980s and reopened in 1988, replacing the old-fashioned cages with naturalistic environments.

    Plastics remain one of the most - used materials for making many things. Things made of plastics can be very strong and last a long time. Plastics are also much lighter than metal and can easily be formed into different shapes. Plastics can take hundreds of years to break down on their own. And very few kinds are highly recyclable.

    A team of researchers working at the US Department of Energy says it has created a kind of plastic that could lead to products that are 100 percent recyclable. It recently reported the discovery in a study in the journal Nature Chemistry.

    The researchers say the new material is a plastic polymer (聚合体)called polydiketoenamine, or PDK. The team reports the material can be broken down in parts at the molecular (分子的)level. It can then be built up again to form plastics of different shapes, textures and colors. The researchers say this process can be repeated over and over again—without the plastic material losing any performance or quality.

    "Most plastics were never made to be recycled," lead researcher Peter Christensen said in a statement. " But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective. "

    Many plastics have different chemicals added to them to make them more useful and powerful. The problem is that these chemicals attach to the monomers (单体), which remain in plastics even after the material gets processed at a recycling plant. The research team reported that, with the newly discovered PDK material, the monomers could be recovered and separated from any chemical additives.

    Next, the researchers plan to develop PDK plastics "with a wide range of thermal and mechanical properties. These plastics could be used for many kinds of cloth, as well as things such as 3D printed materials and foams. In addition, the team is trying to include plant - based materials in the process.