If you look at the top of your phone, you’ll usually see a little symbol that says 3G or 4G. The “G” stands for the “generation(代)” of your mobile network. But these symbols will become things of the past after 5G networks fully arrive.
　　On march 30, Shanghai vice-mayor(副市长) Wu Qing made the first 5G video call on a Huawei Mate X smartphone, CGTN reported. Shanghai has also become the first city in China to start testing 5G networks.
　　About 100 times faster than 4G networks, 5G will let people download and upload data faster than ever before. But 5G won’t just bring faster mobile Internet. People can use it for many other things as well.
　　For example, 5G will help to make self-driving cars safer. Today’s self-driving test cars have one problem-lag. When the car “sees” an obstacle(障碍物), it sends this information to a data center and receives instructions.
　　However, it takes time to send and receive this information. With this kind of lag, the cars might crash because they don’t receive instructions in time. With 5G, this lag will be greatly lowered, making the cars safer, according to CNN. 5G could also be used to power the Internet of thing (IoT, 物联网). This refers to a large online network that connects all things and people. Fast Internet speeds will be the key to developing this technology.
　　The IoT could be used in a lot of ways. For example, with IoT, your refrigerator could automatically(自动地) place an order online for eggs when it finds that there are no eggs left inside.
Who is building the network?
　　China is racing to build a nationwide 5G network. China’s biggest telecom(电信) companies—China Mobile, China Unicom and China Telecom—are working on test runs of 5G systems in 17 cities across the country. China is set to become the world’s largest 5G market, with 460 million users by 2025, China Daily reported.
51. In which city was 5G tested for the first time?
A. Beijing. B. Shanghai. C. Shenzhen. D. Guangdong.
52. We can infer from the story that____________________.  
A. 5G is all over China B. there are no symbols at the top of our phones
C. we can now buy self-driving cars D. 5G networks are much faster than 4G or 3G
53. The underlined word “problem-lag” means ________________.
A. 问题 B. 困难 C. 滞后问题 D. 益处
54. The writer uses self-driving cars as an example to __________________.
A. explain how self-driving cars work
B. show us how advanced self-driving cars are
C. warn about the possible dangers of self-driving cars
D. explain how 5G’s fast speed can be helpful
55. According to the story, the IoT is ________________________.
A. a robot that can do housework
B. an online store where you can buy anything
C. a large online network that connects things and people
D. a type of high-tech refrigerator

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