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.

    Going camping is one of the best ways to get in touch with nature and enjoy the beautiful outdoors. However, thorough plans before a camping trip may be boring. Just follow these simple camping suggestions to make your trip safe and rewarding.

     Selecting a suitable tent

    {#blank#}1{#/blank#}When determining the size of your tent, you should take into account the number of campers as well as the camping equipment(设备) necessary for your trip. There should be enough room in the tent for the camping equipment.{#blank#}2{#/blank#}

    Importance of food

    While camping, you will need enough food to give you enough energy for your outdoor activities. {#blank#}3{#/blank#}You should use a two-burner stove to do all your cooking. Insist on simple cooking during your trip to reduce cooking time.

    Enough sleep.

    All campers should have enough sleep during the night. Nights are generally cooler than the days so you need to have enough warm clothes to feel comfortable to sleep during the night. {#blank#}4{#/blank#}Extra air mattresses(气垫) may be included in your camping equipment to make your bed more comfortable.

    {#blank#}5{#/blank#}Keep these camping suggestions in mind and make sure you are fully prepared to enjoy your camping trip.

A. When buying a sleeping bag, check that you feel comfortable in it.

B. The best camping trips belong to those people who prepare the best.

C. The comfort level in a tent determines the success of a camping trip.

D. Thus you must have an efficient arrangement for your food preparation.

E. If you have a habit to eat in bed, you might train yourself not to do it during camping.

F. The size is the most important thing you should carefully consider when choosing a tent.

G. It will destroy the mood of the entire camping trip if you don't have enough money.

Evaluating Sources of Health Information

    Making good choices about your own health requires reasonable evaluation. A key first step in bettering your evaluation ability is to look carefully at your sources of health information. Reasonable evaluation includes knowing where and how to find relevant information, how to separate fact from opinion, how to recognize poor reasoning, and how to analyze information and the reliability of sources. {#blank#}1{#/blank#} 

    Go to the original source. Media reports often simplify the results of medical research. Find out for yourself what a study really reported,and determine whether it was based on good science. Think about the type of study. {#blank#}2{#/blank#}

    Watch for misleading language. Some studies will find that a behavior " contributes to " or is "associated with" an outcome; this does not mean that a certain course must lead to a certain result. {#blank#}3{#/blank#} Carefully read or listen to information in order to fully understand it.

    Use your common sense. If a report seems too good to be true, probably it is. Be especially careful of information contained in advertisements. {#blank#}4{#/blank#} Evaluate "scientific" statements carefully, and be aware of quackery (江湖骗术).

    {#blank#}5{#/blank#} Friends and family members can be a great source of ideas and inspiration, but each of us needs to find a healthy lifestyle that works for us.

    Developing the ability to evaluate reasonably and independently about health problems will serve you well throughout your life.

A. Make choices that are right for you.

B. The goal of an ad is to sell you something.

C. Be sure to work through the critical questions.

D. And examine the findings of the original research.

E. Distinguish between research reports and public health advice.

F. Be aware that information may also be incorrectly explained by an author's point of view.

G. The following suggestions can help you sort through the health information you receive from common sources.

    Here are some top tips for world travelers.

    Travel light.{#blank#}1{#/blank#} It's no fun carrying a huge bag around a foreign city. Don't take too many clothes and avoid heavy books and electrical equipment.

    {#blank#}2{#/blank#} Always keep your passport on you in an inside pocket or special travel belt. There may be thieves about. It's a good idea to make a photocopy(复印件)of your passport and travel documents.

    Transport sense. Don't let go of your bags on the train.{#blank#}3{#/blank#} There are always thieves on public transport. If you want to sleep, tie your bag to your arm. When you take a taxi, it's a good idea to ask for the driver's permit. Many foreigners pay too much money because they take unofficial taxis.

    Keep clean. It's a good idea to wear dark clothes because they hide the dirt while white clothes attract it! Make sure you have plenty of clean underclothes and deodorant(除臭剂).{#blank#}4{#/blank#}

    {#blank#}5{#/blank#} You should always be polite and respectful towards the locals. Even if you find their habits and behaviour a bit strange, you shouldn't show your feelings. Remember, you're their guest.

A. Be polite.

B. Keep your documents safe.

C. You should carry a spare bag.

D. You don't want to smell bad!

E. Keep them with you at all times.

F. Make sure your bag isn't too heavy.

G. It's a good idea to wear similar clothes to the local people.

    The first men and women came to Britain over two and a half million years ago. {#blank#}1{#/blank#} But the British Isles only became islands separated from the rest of Europe about 8, 500 years ago, when melting ice formed the English Channel!

    3,000 years after Britain became an island, new tribes who came by boat from the mainland introduced farming.{#blank#}2{#/blank#}Many of these man-made hills can still be seen.

    Later on, people learned to build stone monuments. The most amazing is Stonehenge, a circle of huge stones begun about 4,500 years ago. Stonehenge is the world's most famous prehistoric monument. {#blank#}3{#/blank#}

    3,000 years ago the climate in Britain became colder and wetter than before. {#blank#}4{#/blank#} A bit later iron started to be used for tools and weapons instead of bronze. Knowledge of ironworking may have been brought by the Celts, a new wave of immigrants who started to arrive from southern Europe in about 500 BC.

    What we know about the first people in Britain has been worked out by archaeologists from the remains they left behind them. Pytheas, a Greek, was the first person who could read and write to come to Britain. His visit was in about 330 BC, over 2, 000 years after Stonehenge was begun. Unfortunately, what Pytheas wrote has been lost, so we don't have any written record of Britain until the Romans came. {#blank#}5{#/blank#}

A. That was almost 300 years after he did!

B. As a result, people had to move down from high ground.

C. Because of the climate change, much of the ice has melted.

D. Many archaeologists believe that Britain was once covered by ice.

E. These tribes built earthworks for protection and as tombs for their dead bodies.

F. They were hunters and gatherers of food, who used stone tools and weapons.

G. We don't know what it was used for, though many different suggestions have been made.

    If you're thinking about studying abroad, but aren't sure how to convince your parents or yourself, here are some of the best reasons why spending a semester or year overseas is a smart and fun thing to do.

    {#blank#}1{#/blank#} Want to impress potential employers? Companies around the world continue to invest in the global market, and prefer to hire employees who have international experience. Not to mention the knowledge of a second language. Your resume (简历) will stand out from everyone else applying for the same position.

    Learn foreign languages. Language teachers say being immersed (沉浸) in a culture that speaks the language you want to learn is the quickest and most effective way to learn it. {#blank#}2{#/blank#} As globalization brings the world together, it's important to be competent in more than one language.

    Experience different cultures. Immersing yourself in a totally different culture is powerful. You'll experience things like trying different foods, celebrating traditional customs, and learning the history of another country. A person's culture reflects beliefs and values that influence their way of life. {#blank#}3{#/blank#}

    Expand your worldview. Previously held beliefs about foreign countries will change once you've been abroad. {#blank#}4{#/blank#} It can be surprising just how much you know is slightly biased (有偏见的), based on where you're from. It's also a unique opportunity to educate others on your country！

    Earn money! {#blank#}5{#/blank#} We are pretty lucky that English is the international language of business. It's an important language that many foreigners want to learn. You can get paid for teaching, interpreting, or translating English while you're studying abroad.

A. Discover what you want out of life.

B. Improve employment opportunities.

C. You can actually earn income while you study abroad.

D. You'll gain a completely new view on your own country  too.

E. You'll gain an understanding of this that can't be taught with books.

F. Mastering a foreign language opens up all kinds of new opportunities.

G. You'll miss your friends who will want to share their culture and ideas with you.