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.

    Here is a record of the discussion about AI (artificial intelligence) conducted by several scientists:

    Scientist A: I would say that we are quite a long way off developing the AI, though I do think it will happen within the next thirty or forty years. We will probably remain in control of technology and it will help us solve many of the world's problems. However, no one really knows what will happen if machines become more intelligent than humans. They may help us, ignore us or destroy us. I tend to believe AI will have a positive influence on our future lives, but whether that is true will be partly up to us.

    Scientist B: I have to admit that the potential consequences of creating something that can match or go beyond human intelligence frighten me. Even now, scientists are teaching computers how to learn on their own. At some point in the near future, their intelligence may well take off and develop at an ever-increasing speed. Human beings evolve biologically very slowly and we would be quickly substituted. In the short term, there is the danger that robots will take over millions of human jobs, creating a large underclass of unemployed people. This could mean large-scale poverty and social unrest. In the long term machines might decide the world would be better without humans.

    Scientist C: I'm a member of the Campaign to Stop Killer Robots. Forget the movie image of a terrifying Terminator stamping on human skulls and think of what's happening right now: military machines like drones, gun turrets and sentry robots are already being used to kill with very little human input. The next step will be autonomous “murderbots” following orders but finally deciding who to kill on their own. It seems clear to me that this would be extremely dangerous for humans. We need to be very cautious indeed about what we ask machines to do.

    Spending as little as $ 5 a day on someone else could significantly boost happiness, the team at the University of British Columbia found.

    Their experiments on more than 630 Americans showed they were measurably happier when they spent money on others—even if they thought spending the money on themselves would make them happier.

    "We wanted to test our theory that how people spend their money is at least as important as how much money they earn，" said Elizabeth Dunn，a psychologist at the University of British Columbia. They asked their 600 volunteers first to rate their general happiness，report their annual income and detail their monthly spending including bills, gifts for themselves, gifts for others and donations to charity.

    "No matter how much income each person made，those who spent money on others reported greater happiness, while those who spent more on themselves did not，" Dunn said in a statement.

    Dunn's team also surveyed 16 employees at a company in Boston before and after they received an annual profit sharing bonus of between $ 3, 000 and $ 8, 000. "Employees who devoted more of their bonus to pro­social spending experienced greater happiness after receiving the bonus, and the manner in which they spent that bonus was a more important predictor of their happiness than the size of the bonus itself，" they wrote in their report, published in the journal Science.

    They gave their volunteers $ 5 or $ 20 and half got clear instructions on how to spend it. Those who spent the money on someone or something else reported feeling happier about it.

    "These findings suggest that very minor changes in spending allocations—as little as $ 5—may be enough to produce real gains in happiness on a given day，" Dunn said.

    Medicine is the most noble of all the arts, but owing to the ignorance of those who practice it, and those who inconsiderately form a judgment of them, it is now far behind all the other arts. Their mistake appears to me to arise principally from the fact that there is no punishment for the practice of medicine except disgrace, and that does not hurt those who are familiar with it. Such persons are like the figures introduced in tragedies, for as they have the shape, and dress, and appearance of an actor, but are not actors, so also physicians are many in title but very few in reality.

    Whoever is to acquire a competent knowledge of medicine ought to process the following advantages: a natural character; instruction; a favorable position for the study; early tuition; love for labor; leisure. First of all, a natural talent is required, for Nature leads the way to what is most excellent; then instruction in the art takes place, which the student must try to adopt by reflection, becoming an early pupil in a place well adapted for instruction. He must also bring to the task a love of labor and perseverance to ensure the instruction takes root.

    Instruction in medicine is like the culture of the productions of the earth. For our natural character, is, as it were, the soil; the principals of our teacher are, as it were, the seed. Instruction in youth is like the planting of the seed in the ground at the proper season. Diligent study is like the cultivation of the fields; and it is time which passes on strength to all things and brings them to maturity

    Having brought all these essentials to the study of medicine, and having acquired a true knowledge of it, we shall thus, in travelling around, be respected physicians not only in name but in reality. Inexperience is a bad trait, and does harm to those who possess it, nurturing either timidity or audacity(胆大安为). For timidity reveals a want of powers, and audacity a lack of skill. Physicians who are eager for power or those who are undertrained are not a blessing to a community.

    Those things which are sacred or noble, are to be delivered only to sacred persons; and it is wrong to import them to the profane until they have been initiated in the mysteries of the science.

    The popular image of the mountain climber is of a person carefully climbing a steep cliff with a network of safety ropes, but it is not the only kind. Many climbers now enjoy bouldering. It's more accessible and better for the environment.

    Here is an example of a climber addressing a bouldering problem.

    Figure 1: The climber has two routes she could take, one to the left and one to the right. The left one appears easier because it has a jug within easy reach, but look what happens if she chooses that direction. She gets stuck on the rock and has to go back down. Sometimes that is even more difficult than going up.

    Figure 2: The climber takes the one to the right this time. Using a foothold and placing her right hand in a crimp, she is able to lift herself up and locate other handholds. After only a few moves, she is able to throw her leg over the top of the boulder and pull herself up.

Best Places to Visit in Winter

Rovaniemi, Finland

If you love ice and snow, then you'll love exploring Rovaniemi. Why? Simply because it's one of the top winter destinations in Europe. Sitting in northern Finland, Rovaniemi is the gateway to Finland's famous Lapland — the home of Santa Claus, Rovaniemi is the perfect place to watch the impressive Northern lights, go on a husky ride, or even visit an ice hotel.

St. Kitts & Nevis, Caribbean

If you're looking to escape the rain, snow, and grey skies, then St. Kitts and Nevis is one of the top places to go in the winter. This dual-island nation sits between the Atlantic Ocean and the Caribbean Sea. It has perfect weather all year round, with temperatures of 25℃ in winter. Apart from lying on the beaches, you can also enjoy the Carnival around Christmas, sailing and snorkelling tours, and historical tours of the islands.

Cape Town, South Africa

Cape Town is one of South Africa's most picturesque destinations, with loads of exciting things to do. From visiting the 7th Wonder of Nature, Table Mountain, to surfing the waves of the city's S amazing beaches, there's something for everyone. Cape Town is only a short drive away from the iconic (标志性的) Cape Winelands, where you can enjoy vineyard and winery tours with wine tasting and food pairings.

Lanzarote, Spain

With interesting rock formations, volcanoes, and amazing blue waters, Lanzarote is a top choice for many travellers running away from cold European winters. Lanzarote is the most eastern of the Canary Islands. Expect to find black and red earth, white and golden sand beaches and rolling mountains. The average weather stays around the 20℃ mark, so you can work on your tan without worrying too much about sunburn.