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.

    Booking a trip on an online travel site is convenient, but comes with its own set of problems.

    They know who's going to spend more.

    Last year, US travel research company Orbitz tracked people's online activities to test out whether Mac users spend more on travel than PC users. It turns out that on average, Mac users lay out US $20-30 more per night on hotels. As a result, online travel sites show these users more expensive travel options first. To avoid paying more, sort results by price.

    Their software doesn't always link to the hotel's system.

    A guaranteed reservation is almost impossible to come by anywhere — but the risk of your flight or hotel being overbooked increases with third-party providers. The middleman's software isn't immune(防护作用的) to system errors, so always call the hotel or airline to make sure your booking was processed.

    Don't be fooled by packages: Often, they're low-end items grouped together.

    Ever notice how travel sites recommend a hotel, a rental car, and tour package all in one click? These deals usually feature travel that no one wants, like flights with multiple layovers(中途停留). Check the fine print.

    Once your trip is purchased, you're on your own.

    An online travel agency can't provide assistance the same way an agent can if a flight is cancelled or a room is substandard. Basically, when you arrive at the airport or hotel, you're just another customer who booked at the lowest rate.

    “The failure to play is now a serious issue and it calls for action for change,” says Sir Ken Robinson, a leading expert in education, creativity and human development. This is the driving force behind Outdoor Classroom Day—a global teacher-led campaign, supported by Dirt is Good, a company producing daily chemical products.

    Outdoor Classroom Day, taking place on 17th May and 1st November this year, will see schools around the world swap the inside for the outside and take learning into the playground and beyond to make playtime a key part of the school day. This might involve using natural objects like stones to do sums, or going on an insect hunt to encourage curiosity. By now, Outdoor Classroom Day has grown from a grassroots movement to a global campaign that is expected to benefit five million children and over 40,000 schools from all around the world in 2018.

    This is helping to change the trend that sees many schools selling up or building on their playgrounds and cutting back on playtime to make more room for academic studies, while at home children's lives are increasingly filled with organized activities intended to help them learn. Today globally 61% of parents surveyed in the Dirt is Good Qualitative Study said that children don't know how to play without using technology.

    Outdoor Classroom Day is making playing time happen, with 22% of participating schools having increased their playtime since joining the campaign. 93% of teachers surveyed saw improvements in children's creativity after playing outside, and 97% believe that time outdoors is necessary for children to reach their full potential.

    Scientific studies show that real play—the active, physical, self-directed play—is essential for children to develop key life skills that are not taught elsewhere. Few would question the value of developing creativity, leadership, resourcefulness, and curiosity.

    You can't always predict a heavy rain or remember your umbrella. But designer Mikhail Belvacv doesn't think that forgetting to check the weather forecast before heading out should result in you getting wet. That's why he created lampbrella, a lamp post with its own rain sensing umbrella.

    The designer says he come up with the idea after watching people get wet on streets in Russia. “Once, I was driving on a central Saint Petersburg street ad saw the street lamps lighting up people trying to hide from the rain. I thought it would be appropriate to have a canopy(伞蓬)built into a street lamp.” he said.

    In addition to the rain sensor, there's also a 360°motion sensor on the biberglass street lamp which detects whether anyone's using the lampbrella. After three minutes of not being used the canopy is closed.

    According to the designer, the lampbrella would move at a relatively low speed, so as not to cause harm to the pedestrians. Besides, it would be grounded to protect from possible lighting strike. Each lampbrella would offer enough shelter for several people. Being installed at 2 meters off the ground, it would only be a danger for the tallest of pedestrians.

    While there are no plans to take lampbrella into production, Belyacv says he recently introduced his creation one Moscow Department, and insists this creation could be installed on my street where a lot of people walk but there are no canopies to provide shelter.

    In China, there are more and more people leaving the countryside to hunt for jobs in the cities, because the countryside is much poorer than the city, and often there isn't much work there. Services such as hospital and transport are usually much better in the city than in the countryside. They hope that their lives will improve when they move to the city.

    But in the big cities of Europe like London or Paris, people are moving out of the city. These rich families want to live a quieter life. They are tired of the noise and the dirt of the city, and they are tired of the crowded streets, crowded trains and buses. They don't want to live in the cities any more. They want a house with a garden in the countryside, and breathe the fresh air there. So they move out of the cities. Some don't go very far, just a little way out of the city, to the towns near the cities. Other people move to the real countryside with sheep, cows and green fields. There they start new lives and try to make new friends.

    Not all those who move from the city to the countryside are happy. After two or three years, many people who have done this feel that it is a big mistake. They don't make so much money and there isn't much work to do. People in the countryside are different and aren't always very friendly. As a result, quite a lot of people who have moved to the countryside move back to the city. “It's wonderful to see crowds in the streets and cinema lights.” they say.

The Moon Festival is also known as the Mid-Autumn Festival. It is celebrated on the 15th day of the{#blank#}1{#/blank#}(eight) month of the lunar calendar. It's a day to get together with your relatives, admire the moon, and enjoy mooncakes. Here is one way to enjoy a Chinese Moon Festival—cook for the Moon Festival.

Treat your relatives and friends with mooncakes. No Moon Festival is complete{#blank#}2{#/blank#}mooncakes. You can buy them from a Chinese bakery or make them on your own if you have time. You will send them to relatives and friends as{#blank#}3{#/blank#} (present), so prepare enough mooncakes!

Make mooncake biscuits for a sweet treat. Mooncake biscuits aren't as well-known as mooncakes,{#blank#}4{#/blank#}they can still be a tasty dessert for the Moon Festival. They're cookies made from the same dough (生面团) as you use to form{#blank#}5{#/blank#}outside of the mooncakes. You need to wait for 1-2 days{#blank#}6{#/blank#}you can eat them.

Plan a dinner of tasty and{#blank#}7{#/blank#}(tradition) dishes. A Moon Festival dinner{#blank#}8{#/blank#}(offer) delicious for the whole family to enjoy. Think about how many people you{#blank#}9{#/blank#} (invite) over and start to plan your meal. Many families also choose to eat out for the Moon Festival in order not{#blank#}10{#/blank#}(make) a meal-it's up to you!