根据短文内容，从短文后的选项中选出能填入空白处的最佳选项，选项中有两项为多余选项。

      Secret codes (密码)keep messages private。Banks, companies, and government agencies use secret codes in doing business, especially when information is sent by computer.

     People have used secret codes for thousands of years. {#blank#}1{#/blank#}  Code breaking never lags(落后) far behind code making. The science of creating and reading coded messages is called cryptography.

     There are threemain types of cryptography. {#blank#}2{#/blank#}  For example, the first letters of “My elephant eats too many eels” Spell out the hidden message “Meet me.”

{#blank#}3{#/blank#} You might represent each letter with a number, For example, Let's number the letters of the alphabet, in order, from 1 to 26. If we substitute a number for each letter, the message “Meet me” would read “13 5 20 13 5.”

     A code uses symbols to replace words, phrases, or sentences. To read the message of a real code, you must have a code book. {#blank#}4{#/blank#} For example “bridge“ might stand for “meet” and “out” might stand for “me.” The message “bridge out” would actually mean “Meet me.” {#blank#}5{#/blank#}  However, it is also hard to keep a code book secret for long. So codes must be changed frequently.

A. It is very hard to break a code without the code book.
B. In any language, some letters are used more than others.
C. Only people who know the keyword can read the message.
D. As long as there have been codes, people have tried to break them.
E. You can hide a message by having the first letters of each word spell it out.
F. With a code book, you might write down words that would stand for other words.
G. Another way to hide a message is to use symbols to stand for specific letters of the alphabet.

    Don't you just hate it when you have to take an important phone call and you're surrounded by potential eavesdroppers(潜在偷听者)? You either have to whisper or go outside to keep the conversation private, which is not good. Now Hushme aims to fix this problem by muffling your voice and making you look like Bane in the film Batman.

    Hushme is a strange high-tech mask(口罩)that blocks the sound of the wearer's voice so that people nearby can't hear what is being said. It connects to your phone via Blucetooth and comes with a pair of earphones. When you get a private call, all you have to do is put the mask on and it will do the rest. The pair of thick pads over your mouth does a good job of muffling your voice, but to ensure nothing gets through. Hushme also has speakers that play a variety of sounds when you speak.

    The Hushme mask, which comes in a variety of colors, can be worn around the neck, like a regular pair of earphones, and attaches in front of your mouth thanks to a couple of very powerful magnets(磁铁). It's not yet clear how comfortable speaking with this Bane-like mask over your mouth really is, or how effective its speech muffling ability is, so we know so far is that it makes you look strange. The sound choices for covering your voice currently include wind, ocean, rain, birds, monkey, but new ones could be added in the future.

    Advertised as the “world's first voice mask for mobile phones'. Hushme was showed at CES. At the becoming of this year. Its makers plan to sell it by the end of this year. It will cost about $200.

    Once when I was facing a decision that involved high risk, I went to a friend. He looked at me for a moment, and then wrote a sentence containing the best advice I've ever had: Be bold and brave — and mighty (强大的) forces will come to your aid.

    Those words made me see clearly that when I had fallen short in the past, it was seldom because I had tried and failed. It was usually because I had let fear of failure stop me from trying at all. On the other hand, whenever I had plunged into deep water, forced by courage or circumstance, I had always been able to swim until I got my feet on the ground again.

    Boldness means a decision to bite off more than you can eat. And there is nothing mysterious about the mighty forces. They are potential powers we possess: energy, skill, sound judgment, creative ideas — even physical strength greater than most of us realize.

    Admittedly, those mighty forces are spiritual ones. But they are more important than physical ones. A college classmate of mine, Tim, was an excellent football player, even though he weighed much less than the average player. “In one game I suddenly found myself confronting a huge player, who had nothing but me between him and our goal line,” said Tim. “I was so frightened that I closed my eyes and desperately threw myself at that guy like a bullet — and stopped him cold.”

    Boldness — a willingness to extend yourself to the extreme—is not one that can be acquired overnight. But it can be taught to children and developed in adults. Confidence builds up. Surely, there will be setbacks (挫折) and disappointments in life; boldness in itself is no guarantee of success. But the person who tries to do something and fails is a lot better off than the person who tries to do nothing and succeeds.

    So, always try to live a little bit beyond your abilities—and you'll find your abilities are greater than you ever dreamed.

    While the U.S. is still debating about getting rid of the penny, Sweden is rapidly moving towards abolishing currency altogether. Though this may sound radical(过激的), it is a natural evolution in this digital society.

    Sweden, which was the first European country to introduce banknotes in 1661, has just been working harder to convince its residents that digital payments are a safer alternative to carrying cash.

    Over the years, the idea has gained popularity with residents, especially the younger generation that is much more comfortable with technology. Today many banks don't even have ATMs and some have stopped handling cash altogether!

    Tickets to ride public buses in most Swedish cities can only be purchased via cell phones. Numerous businesses are also moving towards accepting only digital payments. Even the homeless that sell street paper to make ends meet have to start accepting this mode of payment!

    But despite its growing popularity, some people don't like this radical idea. They include the homeless, elderly people as well as those living in rural areas who are still uncomfortable with mobile phones and computers. But the officials are confident that in the very near future, they will be able to convince everyone to move this safe and more cost-effective payment system.

    Sweden is not the only country trying to abolish paper currency and coins. The movement is rapidly gaining ground in Denmark and Finland as well. In 2014, Israel announced a three-step plan to go cashless and just last week the vendors(小贩)of a popular street in Sydney declared they would stop accepting currency from customers. Whether this phenomenon spreads remains to be seen. But one thing is for sure—With increasingly advanced payment systems being introduced every day, pulling out cash is rapidly becoming “uncool”.

    The brain is a remarkable part. It's responsible for thoughts and feelings. Now a new study finds that going through tough times as a kid also can have an impact. The adult brains of people who lived through lots of stress before the age of six—and then became depressed or anxious as teenagers—were different compared with adults who had an easier childhood. It seems that teens changed the shape of their brains by internalizing (使内在化) the stresses experienced years earlier.

    Researchers already knew that the shape and size of a child's brain can change in response to lots of stress. They also knew that adults were more likely to be depressed if, as kids, they'd lived in poverty. Some studies showed that these depressed adults had unusual changes in their brain shape. But no one had tested if the early stress and later brain changes were linked.

    Scientists in England studied almost 500 boys from birth until the ages of 18 to 21. Sarah Jensen is one of the new study's authors. Almost all of the boys her team studied experienced some hard times as kids. And, she concludes, "This is not necessarily harmful." To some extent, that's just life. What can be dangerous, she says, is when children experience too many forms of difficulties. Her team's new data suggest that the tougher the childhood, the stronger the impact on the brain might be.

    What's happening in the world around us relates to how we feel. Her team linked more childhood stress to more depression. Still, she notes, it's possible that if you find support for anxiety or depression, you might be able to prevent the changes seen here. "If you can change the environment, you can change the course of things," Sarah says. So, she recommends, if teens develop anxiety or depression, it's good to ask for psychological doctors to give advice.