If you and your friends wish to share a secret, you can write it in code (编码), and no one else will be
able to read it.
Codes are one way of writing in secret. Ciphers (暗码) are another. In a code each word is written as a
secret code word or code number. In a cipher each letter is changed. Codes and ciphers have played an
important role in the history of the world. Julius Caesar, the Roman ruler who defeated almost all the countries
in Europe about 2, 000 years ago, used a cipher when he sent secret messages to his troops. During the
American Revolution, George Washington"s spies used a kind of code to send him information about the enemy
before his military (军事的) action. In World War Ⅱ, the Americans "broke", or figured out, Japan"s most
important navy codes and got enough information to destroy a powerful Japanese fleet( 舰队).
Storekeepers use codes to mark their goods. The codes show how much was paid for the goods or when
they were added to the stock (商品). Businessmen use codes to hide plans from their business enemies.
Sometimes personal letters or diaries are written in code. Many people enjoy figuring out codes and ciphers
simply as a hobby.
In the 16th century, codes and ciphers were very popular among scientists. They wrote messages to each
other in code so that no one else would learn their secrets. Geronimo Gardano, an Italian astrologer (星相家),
mathematician, and doctor, invented the trellis cipher. He took two sheets of paper and cut exactly the same
holes in each one. Then he sent one sheet, which he called a trellis, to a friend and kept the other for himself.
Whenever he wanted to write a message, he put his trellis over a clean sheet of paper and wrote the secret
message through the holes. Then he removed the trellis and filled the rest of the paper with words that would
make sense. When his friend received it, he put his trellis over the writing and read the secret message.
| Radio Most teenagers nowadays are not regular listeners to radio. They may occasionally tune in, but they do not try to listen to a program specifically. The main reason teenagers listen to the radio is for music, but now with online sites streaming music for free they do not bother, and users can choose the songs they want instead of listening to what the radio presenter/DJ chooses. Television Most teenagers watch television, but usually there are points in the year where they watch more than average. This is due to programs coming on in seasons, so they will watch a particular show at a certain time (as long as it lasts) but then they may watch no television for weeks. Teenagers are also watching less television because of services such as BBC iPlayer, which allows them to watch shows when they want. Whilst watching TV, adverts come on quite regularly (18 minutes of every hour) and teenagers do not want to watch these, so they switch to another channel, or do something else whilst the adverts run. Newspapers No teenager that I know of regularly reads a newspaper, as most do not have the time and cannot be bothered to read pages and pages of text while they could watch the news summarized on the Internet or on TV. Internet Every teenager has some access to the Internet, be it at school or home. Home use is mainly used for fun (such as social networking) whilst school (or library) use is for work. Most teenagers are heavily active on a combination of social networking sites. Facebook is the most common, with nearly everyone with an Internet connection registered and visiting>4 times week. Facebook is popular as one can interact with friends on a wide scale. For searching the web, Google is the dominant figure, simply because it is well known and easy to use. Some teenagers make purchases on the Internet (on sites like eBay) but this is only used by a small percentage, as a credit card is required and most teenagers do not have credit cards. Many teenagers use YouTube to watch videos (usually anime which cannot be watched anywhere else) and some use it as a music player by having a video with the music they want to listen to playing in the background. Mobile Phones 99pc of teenagers have a mobile phone and most are quite capable phones. Usually, teenagers only use their phones for texting, calling. Features such as video messaging or video calling are not used-because they are expensive. Services such as instant messaging are used, but not by everyone. It usually depends, whether the phone is Wi-Fi compatible, because otherwise it is very expensive to get Internet off the phone network. As most teenagers" phones have Bluetooth support, and Bluetooth is free, they utilize this feature often. Mobile email is not used as teenagers have no need; they do not need to be connected to their inbox all the time as they don"t receive important emails. |