1. (2019·三门模拟) 假如你是移动公司的销售人员，一加拿大客人向你购买了手机号码13958583739，请你根据短文内容，回答她的问题。

    Have you ever counted the number of digits (数字) in your mobile phone number? Your number has 11 digits. You may sometimes find it hard to remember your number. That's because China has the longest mobile phone numbers in the world. Why is that?

    The 11 digits can be divided into three parts. Each part has a different meaning. The first three numbers tell you which mobile phone service company it is. For example, 135 is for China Mobile Communications

    Corporation and 188 is for China Unicom. The fourth to the seventh digits tell you where the number is registered (注册). And the last four digits are random (随机的).

    The main reason for using 11 digits is that we have the largest population in the world. We once had 10 numbers. But as our population grew, there were not enough numbers for us to use. So we began to use 11 digits starting from 1999. Eleven digits can be used to make tens of billions of mobile phone numbers. That's enough for each person to have seven or eight phone numbers to use in China.

    And mobile phone numbers can be recycled. Usually, the service company will reuse a canceled number after three to six months. If you call a number that you haven't contacted for a long time, you may find that its owner has changed.

    Besides China, Britain and Japan also use 11-digit mobile phone numbers. But their numbers always start with 0. So they cannot create as many numbers as we can. Countries like the United States, Australia and India use phone numbers with 10 digits. Canada's mobile phone numbers are perhaps the shortest in the world: they use seven digits.

Canadian: In my country, the mobile phone numbers use seven digits. Why does this mobile phone have 11 digits —13958583739? Salesman: We have the largest population. Besides China,  also use 11-digit numbers. Canadian: What do the numbers mean? Salesman: The number  tells you which mobile phone service company it is. The fourth to the seventh numbers tell you the                          of registering it. The number  is random. Canadian: Can you  the phone numbers? Salesman: Yes, after three to six months.