In many high schools，there are strict rules about using mobile phones. If your phone rings in class，for example，the teacher will be very angry.
   Every mobile phone has a ringtone (铃声). It tells you that someone is calling you. Now，there is a ringtone called “mosquitotone (蚊子铃声)”. Using it，students can receive calls and text messages (短信) in class but the teacher will not realize what is happening. How?
   Mosquitotone has a special sound. Only children and teenagers can hear it. As we get older，we are unable to hear some sounds with high frequencies (频率). As a result，a child or teenager can hear the mosquitotone ringtone, but it's_inaudible_to someone 20 or older.
   But sometimes，people over 20 can hear the ringtone. One British student's phone uses mosquitotone. In class，the student's phone rang. The 32­year­old teacher looked at the student and became unhappy. “I heard that. You know the rule：no mobile phone in class.”
   Not all the students are interested in mosquitotone. Jerry Jones，a high school student of 17，says，“Using mosquitotone too often is bad for our hearing. I may use it for pleasure，but not in class. It's unfair to the teachers！”
   What do parents think of mosquitotone？“I think it is perfect for places like movie theaters，” says Connie Neeson,44.“Think about it. Yon're watching a film and someone's mobile phone rings. Mosquitotone is good because many people don't hear it. However，it also has a bad influence on their study if students use it in class.”

Subway

    A subway is not just an important form of transport. It is also a window for other people to learn about local cultures.

    Beijing, China

    The Beijing Subway was opened in 1969 and is the oldest subway system in China. It has added some modern technologies. All stations now have touch-screen maps. In some stations, people can also see traditional Chinese cultures. For example, on the walls of a few stations of Line 8, there are some pictures of blue and white porcelain(青花瓷）.

    Stockholm, Sweden

    The system of the Stockholm Subway has 100 stations in use, of which 47 are underground and 53 above ground. The first subway line for Stockholm was opened in 1950. The Stockholm Subway is well-known for its decoration of the stations. It is called the longest art gallery in the world. Over 90 percent of its stations are decorated with paintings. A few stations are decorated with red bedrocks（岩床）. This makes you feel as if you are in a cave.

    London, UK

The London Underground or the Tube is the oldest subway in the world. It was opened in 1863. During World War II, it was used to protect people from German plane attacks（袭击）on London. Now, it is a symbol of the city. There is no air conditioning in the trains, so it is very hot in summer.

    New York, US

The New York City Subway has the most extensive public transportation system in the world, with 469 stations. It is also one of the world's oldest public transit systems. The New York City Subway runs 24 hours a day. It has an express train on almost every line. You can get to your destination(目的地）promptly. The trains themselves are full of fun; you will see people doing moonwalk dances like Michael Jackson, playing the guitar and singing.

    The street food stands（摊）are very popular in Korea . They take their name from the two kinds of hot foods they sell : Dukbokgi and Odeng .

    Dukbokgi is a spicy hot food made of rice cakes and some vegetables . These rice cakes are finger-shaped . They are white , and they are about ten centimeters in length（长度）. They are mixed with sliced vegetables in a pan with a spicy red dressing（调料）. Fifteen minutes later , they are ready to eat . Odeng is made of ground fish . It comes in many shapes : some are square（正方形）, others are round , and still others are stick style . You can buy big or small ones . At these food stands , you can also eat Odeng , which has been boiled in a pot . It is served on a long stick so can eat it easily .

    The food sold at these stands is not expensive , compared to what other foods in Korea cost . Each Dukbokgi and Odeng costs about twenty to fifty cents , depending on the owner .

    Each food stand has its own recipes（菜谱）for its food ; for example , some like to add sugar or other special ingredients（材料）in the food . Usually , there is just one owner , but if the food stand is big , there may be two or three owners .

    When I was an elementary school student , I used to stop at street food stands every day after school to eat street food because I like it so much .